GIOK!!!!!
Sorry to shout but I had EXACTLY THE SAME THING, and what was worse, the processor useage kept rising during each PC access.

I had a year of hell with it till I discovered it was to do with the Anti-virus running all the time. As soon as I disabled the packaged Internet Security & Firewall & enabled Windows XP firewall & Security, everything started working properly again. I had to disable via Windows Services (through administration tools if I recall correctly).

There will be 5 types of svchost, they're Windows programs & should all be running properly when you've got this sorted. Sounds like your set-up is the same as mine, Nvidia is my graphics.

If you do try this, please ensure you enable the Windows Firewall before reconnecting. The Windows XP SP2 security package works well. I also have a tracker on my Startup programs, and Spybot which sorts adware etc. These are all good things to have. Keep checking your task processes though, it's good practice!!