The 4 computers are/were:

P4 1.8 Ghz XP
AMD 2400+ XP
AMD 2500+ 2000
AMD 1700+ Laptop XP

I think it may have also happened to a P3 933 Mhz running ME. That machine is long gone.

Video boards are various Nvidia and ATI models. The laptop has some no-name integrated video card (maybe ATI chips).

Memory amounts have been 256 up to 784 Mb

It doesn't matter what (if any) other programs are running on the machines. Watching the processor usage shows 97-100% usage by Poser.exe when Poser 4 is the active program, even if nothing is happening. If I click on a menu it drops down to very low usage. If I do a render it drops down to 60-70%. Some dialog boxes seem to drop it down to 0% while others keep it at 100%

The only thing common other than Poser is a Windows NT based OS (but I'm pretty sure the ME machine also did that same thing).