4gb Ram, 9600GT, E8400 3.0Ghz (OC'd to 3.6Ghz).
Get some dreamcast games and try them out, they'll be even smoother than pcsx2.
MAME will always be MAME, but it's a good thing you put 64bit vista, it's actually noticebly faster. Get the MAMEUI 64bit compile, they even have some benchmarks at the site with a similar setup. Except for some insanely power hungry games (Naomi, System 12, 13, and some others, it should be enough to run pretty much anything you throw at it.

And try some PC games if you've been unable to lately. There's a slew of great shit to play that your machine won't have any problem with. I play mostly everything at 1920x1080 without filters at max quality. Some of the more beastly titles need some tinkering to get smooth framerates, but the videocard can hold it's own very well.

All work and no play makes me..., well, you know the rest.