With regard to Win7, if you know a current college student, ask if they get a deal on a regular license (not a student license) for the OS. Here at my school (a public University in the US) we get Win7 in our choice of either x86 or x64 for the very fair price of only $7. That's right, seven US dollars, which at today's rate is even less! It's available from our on-campus bookstore only. Microsoft gave our Student Governemnt a deal on the license fee. The $7 covers the cost of producing the cd, box, etc. Currently the x32 is in stock and the x64 will arrive soon. The people who have obtained the x32 are very happy with it. I'm going to install an x64 version on a trading box and test it. I'll let y'all know how it goes. Even if I don't keep it on a trading box, I'm sure I'll have it installed on something.
I installed the Win7 x64 after finals and before I left for the holidays and it worked just fine on a dedicated box. I'm not impressed with anything new. If you're on xp I would not make the change all other factors being equal.
My college's partnership with Microsoft lets us buy Windows 7 for $0. Other free products include: Visual Studio (any edition), all other Microsoft OSes, and most other Microsoft software. $7 for Windows 7 is still a pretty good deal though...