My first idea was to boot the Dell, then connect the old drive via USB and just nuke the Windows folder and anything else that looks OS-related. I kinda don't think that will really work, for all kinds of reasons, starting with a probable freeze when it tries to spin up, all the way to questions about how the XP Pro is going to get some kind of map of what's on the old drive. From one angle, it seems it should be really simple - and from another angle, it seems impossible.
If anyone has done anything like this, it would sure be nice to get some pointers on what to watch out for and how to make it as painless as possible. As far as available resources, besides the 2 computers, I also have an external HD that has about half the capacity of the drive I want to convert. I also have Acronis True Image software, which let me create an image of the XP Pro system that I can load onto the external drive to make it bootable - if the old machine will let me boot that way, which I haven't tried. The old machine can be booted from CD but I haven't yet gone down the road of thinking about how to make a bootable CD or how exactly I would use it if I had one.
Any ideas or comments?