Well, that video card is plenty good... Should last for a while still until the DX9 games start becoming mainstream.
I would definitely upgrade the processor and memory.
Get a couple of 512 sticks of PC3200 or PC3500... something like that.
Your motherboard can handle processors with a FSB speed of up to 333mhz... So, I'd think about getting an XP2500 Barton, which if you're into overclocking, this thing does it great.
I'm not into overclocking, so If I were you, I'd think about maybe an XP2600 to an XP2800...
That should speed things up nicely.
EDIT: Yes, Check to make sure you don't have too much stuff running in the background first... That's a good idea.
What OS do you have?