Can you post a screenshot using the PrintScreen (Prt Sc) button on your keyboard and pasting it into paint or another image editor?
This is the main computer at home correct?
If it's slow on XP, it'll probably be even slower on 7. So I'd upgrade that one. If the Home Premium works fine, it should run a little bit faster on 7 since 7 is better with resource utilization.
Windows 8 is an interesting interface. Personally, I'm not a fan of them trying to remove the start bar. It has been in every version of Windows I've used. But the biggest issue is that SQL2005 Express, which AC uses is incompatible, with Windows 8. So I would avoid that. If you buy now and AC does decide to upgrade it. They do have an upgrade program which lets you get Win 8 for $15 or something. Personally, I'd get the Win 7 and then save the Win 8s for future use. I already have the RTM Version of it. Should hit the shelves late October.