For the question about HP Windows recovery disks (I think Compaq was similar), from my experience having worked with about a dozen models using Win98se and WinMe, they had at least a few "groups" of models that used different CDs. My impression is that the better, more expensive models had CDs different from the economy models. I assume that the CD contained code that read the mainboard to verify it was really that manufacturer's computer and some BIOS code identifier. If correct, then you're stuck if you replace the MB with one from another source and want to use the company's recovery disk later on.
Every time we had to replace a drive we had to pop in several CDs before we got one to work. Tired of that hassle, I finally took a few hard drives, hooked them up one at a time to a workstation, then ran my most recent compatible CD and copied the install files onto each drive. At the point where it said "Please remove recovery CD and reboot computer", I just turned it off and put in the next drive. That way when a hard drive dies and I need a format/recover, I just pop in one of those "prepared" ones and I am done in a very short time.