I got the windows 7 dvd and installed it on my computer. ( I previously had vista home premium) When I was done installing it I checked and I had 32bit OS. I wanted 64. How do I change it? And will it involve wiping my hard drive?

im going to make a network for 20 users and every user needs windows 7 ultamite 64 bit and microsoft office 2007 and i want to buy them as a batch not individually, so i want both of their costs including licensing. and if you find any prices please paste the link. thank you.

I want a Vista 64 bit OS, but want to know the difference between Vista Home Premium and Vista Ultimate.
Who does each version cater to? What type of user for each?

I just recently got a computer that has windows 7 on it. I heard that you could get windows xp on windows 7. I would like to know how to have windows xp on windows 7. Thank you.