It could be the way it handles OpenGL. The [updated] graphics driver, that is.
I'm running Vista SP1 Business (same as Home Premium in all the respects that count), Intel Dualcore E5200 2.5ghz, a Sapphire ATI Radeon HD3450, with 3gb ram, and it all loads just fine.
If ATI uses the same opengl drivers for all their cards (which I assume they do), then the problem could lie in not having enough ram. Unfortunately, there's no way to fix this short of upgrading.
You could also check other aspects of your pc's performance. Stuff like registry, background apps, network activity, etc. Maybe you just have a virus
