Something really fishy is happening with XP to prevent other OSes from coexisting with it.
As I speculated before, I think some DLLs are getting created/moved on the fly, in the XP boot process.
I've seen STOPs in NT when the CDROM was not available after the first stage of installation, but only SCSI CDs on obscure controllers. Put in a generic ATAPI CDROM and go from there. I'm sure the driver disk option when installing is still there, no? (No XP around here any more...)