Let me know, how dirty it was...I have clean out the computer with compressed air which wasn't to bad (the worst parts were the fans and heat sink) the computer is STILL freezing up and the temp of the cpu socket running at 65.0C. The first time i booted up the computer after the clean it completely froze upon START up and had to reboot.Does this mean i need to replace the main board??Did you re-install the MBoard drivers after your last XP install ? ?
What make and wattage is the PSU and how old is it approximately ? ?
All drivers have been installed after a clean xp installation, the wattage for the psu is 450W (about a year old)

My specs are

Intel P4 3.06Gig (4 years old)
2Gig if ram (4 years old)
2 x 160GB HDD's (4 years old)
Asrock P4I65G Mainboard (3 months old)
Nvidia GeForce 7300 GT 512MB (3 months old)
DVD-RAM Drive (1 year old)

Have i got a wattage shortage??Do a memory test....

http://www.memtest86.com/

Ok i ran the memory test from memtest86.com after about 5 or 6 seconds the test crashes showing half of the screen black and the other half blue with parts of the test?Either the RAM is bad...or it's not SEATED PROPERLY...
As always remove all power sources when working inside the case and take anti-static precautions.