Need help planning a trip to Europe

[BWebb]

The title says it all. I have never been, so I'm open to any ideas. Some info, I can travel between Valentine's Day and the end of March (Delta has some good deals right now). I will probably spend 7 days there (2 more days traveling). Not sure if I'm going to be going alone or with friends, I kind of just decided I want to this right now. I would like to see more than one major city while there, but I don't want to rush around barely spending time anywhere. Three cities sounds about right. I'll be doing it on a budget, meaning hostels as much as possible. I'm under the impression that staying in hostels while traveling in Europe is a good experience, is this wrong?

So, what are the best cities to visit, based on easy of getting there, things to see/do and overall experience? Anything I should know about that I probably don't?

I have very limited knowlege on the subject, so any suggestions/recommendations/comments you can make based on this info will be greatly appreciated. If I left anything out that will be useful to know, just ask. BTW, I'm 26 years old.