I went ahead and did a little bit of research on your setup there. Looks like your only running 512mb of RAM with S3 Unichrome integrated graphics. So to put it bluntly your system is not up to the task of playing games at a decent level. All hope is not lost. However it does require you open up your wallet. For the video card I recommend you go with this:
It's too bad you are stuck with an AGP slot. That's pretty much the best bang for the buck i can find for an AGP video card.
I would also suggest buying another stick of RAM if you can afford to. If you want to do that as well i will need detailed specs on the RAM itself to see if i can find a match for it. Otherwise you will want to go with a new set of matched ram.
Just buying the video card will show a HUGE improvement in gaming. On-board graphics REALLY suck. Right now you have an on-board S3 unichrome gpu that uses your system memory (that's not good). Graphics cards have their own on-board memory. So by using a video card instead of on-board video you will be freeing up 64mbs of system memory as well as a graphics processor that can handle just about anything there is out there right now.