Ok my current spec is as follows:

AMD X2 64 3800+
2GIG ddr dual channel
250gig HD
160gig HD
120gig HD
Geforce 7900gt 256meg

Now i can play most new games but not that high FPS... If i was to upgrade my graphics card to say a geforce 8800gt would i notice a big performance difference or would my CPU be bottlenecking it?

Your memory will turn out to be a bottleneck since it's DDR. I'm not really well versed with AMDs, but I'm fairly certain it won't be as much of a bottleneck as the bandwidth of your memory. Some DDR2 800 or 667 RAM will perform much better. Granted, you'll have to get a new motherboard unless it supports said RAM types

Cheers

Mmmm ok, also my Motherboard has 2 8x pci-e slots and not 2 16x ones. Even when i have just 1 card in it will only go at 8x speed. Will i be ok running a 8800gt in this slot? will the performance be affected much? i assume it wont unless i am running mega high res's anyway ??

Even if you don't run "mega high res" it won't affect the performance much. PCI-e cards have yet to use the full potential of PCI-e 16x, you might see maybe 2% to 5% less performance when using x8 instead of 16x, but it's hardly anything really notice-able