Your graphics card could be the real problem and the fact you're still using an AGP card instead of a PCI-E card tells me you've not changed it in at least two years, probably four. Try this to see if you get anywhere but be aware your graphics card probably needs upgrading:
Change your V-Sync setting first and see if performance is better or worse. If need be, set anti-aliasing, anisotropic filtering and all other such options to off and see if the game is smooth (do not expect it to look nice). Once it is smooth, assuming V-Sync didn't help, turn on anti-aliasing to smooth the edges and find a happy medium. Leaving it up to the application isn't wrong as it allows you to use different settings for different games without having to fiddle around with settings constantly - you just set it in the game you're playing.
A good mid-range ATi card is the Connect3D X1950XT which is around £150 BUT needs a PCI-Express slot on your motherboard which yours probably doesn't have as very few motherboards have both a PCI-E and AGP slot. To be honest, using a PCI-E card is the only real way forward if you want to do a fair bit of PC gaming. If, however, you don't mind buying an nVidia card you may want to look
here, a GeForce 7600GS for under £100. Try to compare your card to that one though and when looking at the specifications look at the memory speeds and number of pipelines. I would guess the 7600GS is substantially superior to your existing card but check for yourself to make sure....assuming you have the money to spend. Hope this all helps.
