swiss train travel help needed!!

It is 7 1/2 hours to Salzburg by the route you suggested. If you had a Swiss Pass, that would cover you as far as Buchs, Switzerland (border with Liechtenstein) then you would pay for the portion from there to Salzburg.
Your Swiss Pass will get you a 50% discount for the portion of the Jungfaujochbahn above Wengen (free to Wengen). It would also get you a 50% discount on the Schilthornbahn. Another thing to consider is the Swiss Card for 199 chf pp. That gives you free travel from Geneva airport to Interlaken, free travel from Interlaken to Buchs, and a 50% discount on trains while you are in Interlaken.
I would not bother with a 2 country pass. Just get advance purchase nonrefundable discount ticket for Austria. You can also ride a train called Westbahn from Salzburg to Vienna for 23.90 euro/adult plus 2euro per child 14 or under (under 6 free). There is also a family card available in Austria (not sure the cost), then it is 43 euro for the whole family (again, 15 and older is considered an adult).

Sam, how many times have I posted to correct you? The discount with a Swiss pass or Flex pass is 25% above Wengen, not 50%. Please see the synoptic map with the special notation for this route:

http://www.swiss-pass.ch/sites/default/files/pdf/swiss-travel-system-map.pdf

Sometimes the best price from Interlaken to Salzburg is a discount ticket on the direct Zurich to Munich train! bought well n dance on bahn.de to get the savings price. Use your Swiss or fles Pass to get from Interlaken to Zurich.

Aha. Yes, I have the synoptic map on my desk next to my computer. I stand corrected.

Actually the Half Fare Card does provide a 50% discount all the way to the Jungfrau. See validity map link on this page: http://www.sbb.ch/en/travelcards-and-tickets/railpasses/half-fare-travelcard.html

Since you are staying in one place in Switzerland, you can buy the Swiss Transfer Ticket. It will provide your full transportation cost from Geneva to Interlaken and from Interlaken either back to Geneva or to Zurich where you would transfer to a train going to Salzburg. While in Interlaken, the Swiss Transfer Ticket becomes a 1/2 fare card that will provide you a 50% discount to the two mountain tops. No Swiss pass or card will provide 100% coverage to the two mountain tops. 50% coverage is the maximum above Wengen and Muerren. For the Eurail pass, you are only 25% covered (you pay 75% of the fare) of all transportation beyond Interlaken Ost and into the Lauterbrunnen Valley. The postal bus inside the valley does not accept the pass. With minor exceptions, your Swiss pass or card is good only to the Swiss border. When purchasing your ticket to Salzburg, just show your ticket to the agent and they will make the adjustment.

Yes, a Half Fare Card ( or Swiss Card) does provide a 50% discount on the Jungfraubahn. But a Swiss Pass or Flex Pass does not. With those it is 25% above Wengen. It adds up to a considerable difference and it is important to help people understand this.

"While in Interlaken, the Transfer Ticket becomes a Half Fare Care that provides a 50% discount...."

Sorry, but this is wrong. A Transfer Ticket is only good for two journeys, in and out. There are no additional discounts. Larry must be thinking of a Swiss Card, which is a Transfer Ticket PLUS Half Fare Card ( and costs extra).

You tell 'em Sasha, and the Swiss Card is only 199 chf pp. The transfer ticket is 139 chf, so you are only paying 60 chf for the half fare privileges.