Just when you are about to do a backup, 'cos you've been a bit lax for a couple of weeks, it starts acting up. I started getting IRQ_NOT_LESS_THAN_OR_EQUAL BSODs. After hunting around forums, it appeared to be connected to pagefile issues, so I removed and recreated my pagefile.
Then I started getting POOL errors, which quickly escalated to the classic symptom of only getting to mup.sys on boot. Sadly this wouldn't let me boot from an XP CD either. After much faffing, Knoppix came to the rescue. I built an XP installation on another hard drive (with my faulty one unplugged, otherwise it wouldn't do it!) then rebooted with both drives connected, using Knoppix CD. This at least let me get all my data across. I was going to use captive-ntfs to mount my old drive read/write but the screwed up filesystem wouldn't let me.
So today I finally wiped the old drive, reinstalled and am now downloading all the relevant updates. At least I had used Slipstreaming to give me an XP SP2 CD before all this happened, but it still wants many updates, and the amount of downloads I need for my Audigy Platinum is staggering.
The only upside is that all the cruft will be gone and the machine will run faster for a while:-)