You dont even need 12 GB RAM since NONE OPERATING SYSTEM SUPPORTS UP TO 12 GB RAM and cannot use it 100% Also, agree with IcyAero, the GPU is BOTTLENECK beside to other components.
Firstly, 12Gb of RAM is Recognisable due to the x64 Operating System, he even said in the first post. Windows Vista Ultimate x64 can support up to 128Gb of Ram.
Secondly, the ATi Graphics Card actually scores higher than its nVidia counterpart, ATi4650 - 9600GT, They are around the same speed, and it will not bottleneck at all.
Lots of people think Intel is better than AMD, Hell, I was an intel man for years, but I have now used AMD in 2 different machines (That includes ATi Graphics) and it has been no different, if not a little faster than all my intel machines.
AMD Processors are capable of a higher calculations per nanosecond. Don't take your personal opinions into other peoples topics, AMD and Intel are Both very good brands, they are all made of plastic and metal.
The Computer samiir got is fine.
Shaun
PS, I never included a possible solution. Disabling the Frame Limiter would most likely make a difference, also, the Operating System could be responsible, make sure you have Vista SP1 installed or XP SP2 if its XP Pro x64 (SP3 Doesn't work with XP Pro x64 so don't even argue)