Munich-Switzerland-Venice-Florence-Paris -HELP!

First, you have 5 train rides (some long ones) in 10 days. Did you want to see Europe, or just trains and train stations? Sorry for being harsh, but this would be the trip from hell for me. Now, to answer your questions:
To get route information for European trains, the best place is the Bahn Website. This is also the place to get price information for trains starting in Germany (like your first one). For your others, use the website of the national train company for the country your route originates in. For Switzerland, it's Swiss Rail. For Italy, it's Trenitalia; register on the site before trying to buy tickets (no registration needed to browse routes and prices). For info on Italian train prices and ticket options, see Ron In Rome's discussion. For France, use TGV Europe, choose "Great Britain" as your country, and don't let yourself be redirected to Rail Europe (which charges more). In general, you will save money (often a lot of money) if you buy non-refundable, non-changeable tickets in advance.

What exactly is the purpose of your trip through Switzerland? Look on a map. Traveling from Munich to Venice, Switzerland is a significant detour to the west. If you are on a tight budget and you want some Alpine fun, you would probably do better going straight through Austria. Switzerland can easily bust a budget. And by the way, because weather can change rapidly in the Alps, one night stays are not a good idea.

Thank you very much for your helpful links and websites. Alanna

Yeah, definitely avoid Eurail tickets, at least based on the amount of travel you'll be doing, point to point will be cheaper. In addition to the good info already provided, I recommend checking out The Man in Seat Sixty One, which is an excellent site for explaining European rail travel, passes, how to get cheaper fares, how to book tickets and avoid Eurail, etc, etc.
And sorry to rain on your parade, but I have to echo previous comments...with only 10 days, the itinerary you have will leave you very little time to see/do anything

Is TGV Europe the high speed trains?

TGV ( Train à Grande Vitesse, or High Speed Train), operated by SNCF, is France's high speed train network...

A four-country Eurail Pass would cover all your rides. You would need to buy seat reservations for any trains that require them. However, buying point-to-point tickets will be cheaper. The tgv-europe site shows timetables and fares for all French trains, not just TGVs. You're trying to do way too much. Unless visiting Walchwil is extremely important to you, skip it. Muenchen-Interlaken Ost: Book today on the German Rail site to get a discount fare as low as €49.00. Interlaken Ost-Venezia Santa Lucia: You will travel Interlaken Ost-Spiez-Milano Centrale-Venezia Santa Lucia. Use the German Rail site to see complete timetables. Buy a ticket for a regional train from Interlaken Ost to Spiez when you get to Interlaken. Book Spiez-Milano Centrale today on the Swiss Rail site to get a discount fare as low as 23.00 CHF. Book Milano Centrale-Venezia Santa Lucia today on the Trenitalia site to get a Super Economy fare as low as €9.00. Venezia Santa Lucia-Firenze: Book today on the Trenitalia site to get a Super Economy fare as low as €19.00. Florence-Paris: Don't take the train. Fly Vueling from Florence to Paris Orly. Book today to get a fare as low as €50.00. Vueling is a budget airline. There are limits to luggage size, weight, and number. If you exceed those limits, the fees you'll pay can be as much as the ticket. Be sure to observe the strict check-in deadline. On budget airlines if you don't have a boarding pass in hand when the check-in deadline arrives, your ticket will be worthless and you will have to pay full fare for a ticket on a later flight.

To be even less rushed, do what Tom suggested and skip Switzerland altogether. If you book today on the German Rail site, you can get a discount fare of €49.00 for a direct daytime EC train from Munich to Venice. Or take the direct CNL night train. If you book today on the German Rail site, you can get a discount fare of €69.00 for a bunk in a 6-person couchette, €79.00 for a bunk in a 4-person couchette, or €109.00 for a bed in a 2-person sleeper. All couchettes are the same size. The only difference is in how many bunks are pulled down. Paying an additional €10.00 for a bunk in a 4-person couchette is well worth it for the extra space for both people and luggage.

Wow! Thank you VERY much. I like the idea of the flight. However I am struggling to find Florence Airport anywhere... It must be tiny.
Is it the airport they call Peretola Airport? Alanna

Hi! Thanks for your help, I booked that flight. I see that this airline has extreme reviews, some people are super happy, some people super upset. I hope that there are no problems for us... I tried to check in online (as per your boarding warning), but I got the following error message: ***** You cannot check in online for this booking. The airport you're flying to does not offer the online check-in service. You must get your boarding pass at the check-in desk on the day of your flight. *****
I guess I'l just have to treat it as a normal flight and show up an hour early to check in baggage (paid extra) and get my boaring pass. I have insurance in case anything goes wrong. Alanna

Is it the airport they call Peretola Airport? Yes, Alanna, it is. They have a half decent website in English at http://www.aeroporto.firenze.it/en/

Hi, I'm trying to book the Venice-Florence leg, and the economy options are sold out, this is my only option: ****** Price / Service level Close 2ª CLASSE Image 1ª CLASSE Image BASE Image 90. 00 € 126. 00 € ECONOMY Image Sold Out Sold Out SUPER ECONOMY Image Sold Out Sold Out 2x1 FRECCIAROSA Image 45. 00 € 63. 00 € **** What on earth is a ''2x1 FRECCIAROSA''?
Does anyone know?

From Trenitalia website... "With Frecciarosa 2x1 you can travel with another person (2 people) and pay just one ticket, as long as one passenger is woman and over 12. The offer is valid the whole October 2012 to travel every day of the week from 11 to 14 and the every Saturdays for the whole day. You can purchase the ticket up the day before departure on this website, calling the Call Center (payment number), ticket offices at stations, self service machines and Travel agencies, The offer is valid to travel on all AV Frecciarossa and Frecciargento trains, Frecciabianca and ES* Italia in 1^ and 2^ class and in Business, Premium e Standard service levels. It's not included the Executive service.
The Frecciarosa 2x1 tickets take part into the fidelity programm."

What's your travel date for Venice-Florence?

Hi! Thanks everyone for your help!
Everything is now booked, and I do not think the travelling time is too much. The only thing I am still considering is travel within Switzerland. We saved quite a lot of money not taking the "Eurorail Pass", so I am wondering whether it wouldn't be worth it to just book point-to-point trains within Switzerland. Especially since I booked the cheap rail from Spiez to Milan without the pass already... Any opinions? Thanks again for the brilliant help:) Alanna

Muenchen-Walchwil: Book Muenchen-Zuerich on the German Rail site. Buy tickets for Zuerich-Walchwil when you get to Zuerich. The fare is 18.00 CHF. Walchwil-Interlaken Ost: Buy tickets in either Zuerich or Walchwil. The fare is 40.00 CHF. Interlaken Ost-Spiez: Buy tickets in Interlaken. The fare is 10.40 CHF.