Zahra,
As this is your first trip to Europe, my first suggestion is to pre-read the Guidebook "Europe Through The Back Door". Given your location, you might consider taking a short drive to Edmonds and picking it up right at ETBD.
You could also speak with the experts there regarding your travel plans. Buying the country-specific Guidebooks (or at least browse through them in the Library at ETBD) would be a good idea also. If you're going to buy country Guidebooks, wait for the 2011 editions (some are available now).
Using open-jaw flights is absolutely the best idea! I definitely agree with a previous comment that starting in England would be a good idea, as it will be less of a culture shock, and no language issues (although that point is sometimes debatable!).
Mid-August is going to be PEAK tourist season, so pre-booking accommodations would be a REALLY good idea! September is "fall shoulder season" so it will probably also be busy.
Using a Railpass is not necessarily the best idea. You don't need to decide on that until you have a more-or-less definite Itinerary worked out. One thing to remember with Railpasses, is that these DON'T include reservation fees that are compulsory with some trains (usually the fast trains such as the TGV in France, which travels at 300 kmH).
With a trip of only a month, I'd suggest dropping Greece this time, as it's somewhat "distant" from your other locations and you won't really have enough time. Spain is also somewhat distant, but more manageable with fast trains or budget airlines.
You might also find it helpful to watch "Travels in Europe" on KCTS. The new series (filmed this year) usually air on Wednesday nights at 19:30. Other nights have re-runs, but they're always interesting. There are clips of the shows available on You Tube and other sites.
Good luck with your planning!