Vista - Very annoying freezing with Vista

Heya,

I bought a new computer with Windows Vista Ultimate 32bit in december. Everything was working fine for a while until I realized that my system was lagging.

Every three seconds, System (NT Kernel & System) process takes up 20% of my CPU for a second and then drops back to 0%. This causes FPS drops and/or freezes my mouse and keyboard. This is VERY annoying and it also freezes the sound and pretty much everything that my comp is doing at that moment. This usually happens when gaming but sometimes it even happens when I am listening to music of watching a movie.

I've tried disabling some Vista's processes but with no success at all. Cod2, which worked fine on my 6 year old computer lags more on my brand new computer with lower settings. That's why I'm thinking that it might be a hardware problem but I just do not know how to solve that.

System Specs
HiJackThis log

If you need more information just tell me. I'm not very familiar with hardware stuff but I just need help really bad.

This is the thread process that is using my CPU.