PAR is built on a Win7 PE, but must have had the SATA driver for the other PC or it had the same one. This is the only deal-breaker as far as drivers are concerning when switching. But another important function as I understand it is removing the SID and HID of the source install so that it is accepted to start up by the new hardware. This may have been what was accomplished by it here. I don't think an XP Repair install would do that, only change out drivers.
Someone else may know for sure, but PAR has mainly been promoted here by SIW2, then me, then Kaktussoft wrote his tutorial. I still use it all the time moving images around on home machines, but only for Win7.