I just built my first system. I used a 1.2Ghz athlon and a Asus Geforce GTS card. It's only so I can potter about abit when I'm not a work so I wasn't really bothered about it slowing down with paint fx.
Anyway I tried it this weekend and it's fine - there's a slight delay when the brush first touches the surface but after that it's a fast as photoshop. Woohoo, what a bargain.
I'm a bit cautious about telling everyone else to get one but - it worked for me.