So after working on the problem all day yesterday... well not directly... Much of the day was taken up in trying to restore from a backup unsucessfully, and then to take (successfully... eventually) clean backups off the drive in the laptop. Then much of the rest of the day was spent working around the problem so I could actually, you know, work, at the job, that pays me money...
I finally figured out this morning what was causing the problem. I have a corrupted data partition, on which are stored some critical files. Every time windows accessed some parts of that partition it would start to fail ungracefully, eventually locking up totally.
By booting to a rescue disk, and force mounting the other partition, I was able to get a full backup. Now I just need to wipe it, scan the disk for bad sectors, and recreate it clean so I can reload the data.
In the mean time, I've removed the partition from the volume manager so windows programs can't try and access it, causing another crash. I've moved my critical work data onto the primary partition, and I'm running off that for the work day, until I can do the full cleanup job.
Hopefully the many crashes in between haven't corrupted windows badly enough that I need to reinstall; though I probably should anyway, and will when I have time.