What can make a 2.4GHz run like a 486?

The answer would be XP SP2!
Seriously, I just got a new cheapo hp computer from wal-mart, right? And even though I've used every trick I know of (turn off all effects, use the 'classic' windows style instead of the playskool style) the version of XP home runs like shit on it.

A great example of this is when shutting down GTA 3, the computer routinely slows to a crawl, and whatever windows I have open are painfully, slowly re-drawn.

It will take in the neighborhoood of fifteen to twenty seconds for everything to re-draw itself.

I've tried replacing the video card (with an nvidia one), installing windows 2000 isn't an option...so has anyone else had to deal with speed issues on windows? Any suggestions ("omfgbbq run linux!!!1one" isn't on the table, neither is *BSD) on what I can do to make my 2.9GHz respond like a machine which is >99mhz?

>>1 How much memory does it have?  The behavior you're describing is exactly what I'd expect from trying to run Windows XP in 128MB of memory, regardless of CPU speed (I bet you've got a Celeron, though, and Celerons are lame even at 2+ GHz).  Go up to at least 512MB.  1GB won't hurt, either.  See if that helps.

Also, what nVidia card have you tried?  I'd not expect an old TNT2 or GF2-MX to perform significantly better than the crappy integrated graphics on the motherboard.  And does the motherboard have an AGP or PCI-X slot, or do you have to use a PCI video card whose performance is cut off at the knees by the slow PCI bus?