If at school did not tell you which Vista version you specific need, I guess Vista Home Premium would be good enough.
Rather than an upgrade, I suggest you back up all your important data and do a clean installation, when it comes to prices, if you go with the OEM version, which you can get at Newegg, you can save some cash, the retail version can be transfer into another machine in the future, that is why is more expensive. I'm posting the upgrade retail link too, in case you still want to do an upgrade.
Microsoft Windows Vista 64-Bit Home Premium - OEM $109.99
Microsoft Windows Vista Home Premium Upgrade - Retail $144.99
This is the link to all versions of Vista:
Before installing Vista I suggest you do all the reading you can, so you learn from others, the OS can be successfully install and use, but if you don't want headaches, please do your homework.
