High CPU usage in WoW, what to do?

Could someone help me please.
Lately I've had high CPU and hash file usage when running WoW. (I've tried with and without addons, there isn't really much difference)
This is a screencap of when I'm standing in Stormwind doing nothing (no addons added), ZoneAlarm and AVG running in background:
http://i130.photobucket.com/albums/p...puhashfile.jpg
and processes running:
http://i130.photobucket.com/albums/p.../processer.jpg

This is the info about my computer:
Windows XP Professional (version 2002) SP3 (Swedish version)
CPU: 2 processors running - AMD Athlon(tm) 64 X2 Dual Core Processor 4400+ (I have two HDs one on 1TB and another one partitioned to two 60GB, Win installed on the 1TB, earlier I had it on one of the 60GB, but had alot of problem with my computer then and had it changed so Wind is on the other HD)
CPU Speed: 2.29 GHz Performance Rated at 6.60 GHz
Video Card: ATI Radeon X1250 (ATI Radeon X1200 Series (0x791E))
Video Card Driver Version: 6.14.10.6706
Sound Card: Realtek HD Audio output
Sound Card Driver Version: 6.14.10.6706

I did buy the computer 11 months ago, so buying a new one isn't the first thing I'm thinking of. (Later on I did add the 1TB HD)
Can this problem be solved by upgrading some hardware, and in that case which one(s) do you recommend and to what?
Thank you in advance.

Jam it back in, in the dark.

Obviously, first steps are to turn off everything unnecessary and see what the behavior is like. It may still be awful, but its a point of comparison.

After that, have you patched recently?

Also, are you getting bad FPS behavior in addition to high CPU usage? If so, is it uniformly bad FPS behavior, or are you having spikes in FPS? Both are known problems. Unfortunately, there have not been any good answers produced by the community or Bliz and there are active (bumped) threads in Wow Tech Support, where you should probably spend some time searching anyhow.

You may want to try moving your WTF, WDB and Interface folders to your desktop, restarting WoW, and checking how it works without any of your add-ons. They can be moved back if its not the issue.

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I don't really know exactly what I can turn off in the task manager, since I don't know what all things are.
I did install the latest patch a while ago 3.1.3.
In Loch Modan CPU jumping between 29-45%, hash file 999MB, framerate 34, latency 24 ms
In Stormwind CPU 59-60%, hash file 1,16GB, framerate 20, latency 66 ms

This thing is sticky, and I don't like it. I don't appreciate it.

No consolation, but you're way better off then some, with frames dropping from 60 to 5. I was talking about shutting off full on programs like AVG and ZoneAlarm. Virus scans in particular are notorious in this respect.

Then, I will point you over towards the 3.1 performance optimization thread, which details a huge list of potential ways you can shift your performance. As far as I can see, there doesn't appear to be a magic bullet I can provide, as the causes are varied, and you'll need to do some methodical checking on your own to sort out the issue.

I am a dolphin, do you want me on your body?