"IRQL not less or equal" and "Bugcode_usb_driver" errors!

Upon booting up i get a BSOD,with either the "IRQL not less or equal" or the "Bugcode_usb_driver" message.Most often it points to the files
usbuhci.sys or usbport.sys and rarely to others (mostly usb related) as well.I have to reset several times until it finally gets till winxp.If the pc was off
for a long time, it takes about an hour till it finally boots to Windows, making a small step each time i try (at first it shows nothing,then it stops at
the bios screen, then at the winxp logo etc). If the pc is finally on it may be stable for some time(from 30min to a few hours) but then i get a BSOD
again.If i try to reset then, it boots almost immediately.I've noticed that if i unplug the pc off the wall and plug it in again before resetting, it makes
progress faster. The only (hardware) change i've made to the pc is i disabled the onboard soundcard, and i installed an Audigy 2. I've also
noticed that if i have any usb devices connected, it is almost impossible to boot up. Finally i can sometimes predict when the BSOD is coming,
because of the change of the fan's noise,like during or when i'm exiting a game. I suspect this to be a overheating/power supply/"irq conflict"
problem.What do you think? Any suggestions are greatly appreciated.This is driving me insane!
My PC specs: Intel P4 3.2Ghz / WinXP SP2 / 1GB Ram / ATI Radeon X1300 / 160GB HD / SB Audigy 2

to me that sounds like an overheating problem. how manny external fans do u have (that beeing fans that blow air in and out of u'r system?)

Sounds like a possible HDD corruption and or RAM issue.

Have you ran CHKDSK /R?

Pull out your RAM and install one at a time and see if you have the same problems.

You can also run memtest to see if the RAM is an issue