If your motherboard supports EFI, then there is no reason why Vegas won't install to it.
http://www.pcworld.com/article/235088/everything_you_need_to_know_about_3tb...
Only one hard drive?? You want two drives. Put the OS and Vegas on a 1Tb drive (C) and all of your projects and media files on the second drive. (Not a separate partition of the one hard drive - you gain nothing).
I can't help you with the GPU since I replaced my last Radeon card months ago. (Last, being the operative word).
Steve Mann
MannMade Digital Video
http://www.mmdv.com
