Joint OPS FPS Very LOW!!!!

Hows it going all and thank for your help in advance.

I have a Dell Optiplex 240 P4 1.60 GHz processor, 768 MB RAM, ATI 9800 Pro 256 Vid Card, Win XP Pro and a 20 gig Hard drive (I know I need to upgrade) that is half full.

I get at the most 30 FPS and most of the time I'm at 2-14 FPS.

I have tried everything from tweaks to new drivers and nothing helps.

I have read all over the net but I think I am missing something.

Any suggestions?

Thanks