Help with frame rates

Hi. I'm no expert, so I thought I'd ask here.

I got a new PC in November. The spec is:

Core 2 Duo E6600 @ 2.4Ghz
nVidia GeForce 7950GX2
2GB Samsung DDR2 SDRAM @ 667Mhz
19" analog flat panel monitor (my old monitor, didn't come with new PC)

I've noticed a lot of games (Need for Speed Carbon, Top Spin 2, TrackMania United, The Race - WTCC) struggle with the frame rate at max settings. TrackMania, for example, will only give 60fps @ medium quality, in 1280 x1024. Things like turning shadows and motion blur on seem to be a big problem.

I've made sure the games are all using both cores (Task Manager, right-click process, choose Set Affinity) and in my nVidia control panel I've turned on Multi-GPU (someone else told me about "SLI" options, but I can't see such an option in nVidia's contrl panel - I'm guessing "multi-GPU" is the same thing???)

Do you guys think all the above is expected? Or am I doing something wrong? After spending £1,400 on a PC with no monitor I was kinda hoping for good frame rates with high quality visuals.

Thanks folks

I normally have anti-aliasing set to 4x (that's usually the max available - in TrackMania it has on option for 6x, but it says N/A next to it).

Isn't AntiAliasing all part of a better image quality though?

Would I get a better effect with other options on and AA off?

I did a benchmark at Max settings in (AA x 4) Trackmania, and got an average of 26fps. Turning AA off and still with everything else at Max I got 29.7.