Repeated stop error 0X50

Of all forums I've checked, this seems to be the one with the most solutions--so here's my problem:

I have a computer running XP SP2 that is continually crashing with an error: PAGE_FAULT_IN_NONPAGED_AREA. Ran chkdsk /r /f numerous times. Cycled through all RAM. Ran virus checks. Etc. Etc. Nothing worked so reloaded XP. That didn't solve it either. Lost all hope, decided it must be a bad harddrive and replaced it. Finally, computer worked. Got some stress software called "BurnInTest" and ran it. No problems. Then today I needed some items off the old harddrive so put it back in. Sure enough, crash after crash. So went into safe mode so I could at least copy off the files, which I did successfully. But I noticed it didn't crash after two hours, which is a century in my computer's recent history. So decided to do a little test--ran the stress test in safe mode and came up with no HD errors. So now I suspect HD might not be bad after all!

I've attached my last 5 minidumps. I can't make sense of them. Hopefully one of the many helpful people on this forum can...

You've got a rootkit. See this THREAD (http://www.techspot.com/vb/showthread.php?t=83428&highlight=rootkit).

a1d48000 a1d6f000 vdo_722d_4e59 vdo_722d-4e59.sys unavailable (00000000)

Thanks -- you're awesome! I finally got my computer back up and running. You saved me an HD!