I've been mining for about three weeks.

21M Is a pretty number?

When you check on the pool, does it show successfully processed shares? If so there is just something weird going on in the miner.
As long as the work gets done you shouldn't worry..

I don't currently use AV, i just encrypt anything important and maintain a protected network.

However at work the only product i would ever install on a computer is NOD32..

Are you sure it is the actual miner which is taking upp all that CPU?
I ran GUIminer with my two 5850s on my x4 965BE CPU with three cores disabled and downclocked to about 2.5Ghz just to see what poer usage i got to, but it still only used like 25% of the cpu. I am watching my miner now via teamviewer, it is 50% total CPU, with system idle process having about half and poclbm having a constant 25%...

I can note that I am able to run 720P video from my CPU while mining at full speed without losing hash.. I also have utorrent and some othe rstuff running in the background without affecting the CPU badly.

Hello there, I am a swedish miner, and I seem to be a newb here. Dang.
Hail!