I can't remember exactly if I have booted a WinPE on an Axp but I must have. I would wager that it isn't so much a problem with the CPU but with how the board works. If you are using an ATAPI or SATA ODD, try using a USB one. Or try having your WinPE boot from a USB key. I rarely ever will use a CD to boot a custom WinPE, so I don't have much experience in that. To see if there is an actual problem with those boards and WinPE 3, presumably a Windows 7 RTM DVD would have the same problem, if not SP1.