Any LCD with a response time TOTAL of 20ms or 16ms should be fine for games.
With some LCDs there are problems with dark colors blending in games.
Sony makes a 20ms LCD, forget the model number though.
Obviously other companies make 20ms LCDs too, but I haven't read up on 20ms LCDs in a while.
Hitachi, NEC, Planar, and quite a few others make 16ms LCDs.
All 20ms and 16ms are 17" panels.
All 19" panels I know of are 25ms and up, pretty slow.
About your video card upgrade, don't get any MX (they are pretty much just spruced up Geforce 2's), and don't get the FX5200(ultra or not), it performs worse than your Geforce 3.
5600ULTRA is decent, make SURE it's the ultra version, though, because some manufacturers try to trick you.
As always, the Geforce 4 Ti's are always a good choice.
All depends on your budget.
Just some advice, so you don't get ripped off.