post a DXDIAG report, that will help alot as well........
can get the make of PC, sometimes the MotherBoard, CPU, memory, video, OS, sondcard, etc.....
will let everyone know if it is a proprietory PC or a clone ( Home built type pc )
will tell us how many processes you might be running and your pagefile size as well.........
and if you could swing the money, I would upgrade to minimal Windows 7 home edition 64 bit OS ( preferably Windows 7 Pro or Ultimate 64 bit ) to gain asmuch performance from your CPU, Ram and new Video Card you decide to get, utilizing that dual core AMD processor.....
just my opinion though..... ( I am figuring you have Vista 32 bit )
you going to need a GOOD minimal 500 watt PSU ( 80% + eff. rating ) as well....
get the DXDIAG report and copy/paste top 2/3rds here on the boards ( to this thread )....
good luck......