expgal, have you tried adjusting the hard disk operation mode BIOS setting(s) on the PC that keeps rebooting? I encountered this problem on several different Dell Optiplex workstations in my school district and discovered that if the Windows XP image was created while the hard disk operation mode was set to ATA in the BIOS on the source machine and set to AHCI on the destination machine, the imaging process would succeed, but Windows XP would not boot up. You might benefit from comparing the BIOS settings on the source machine with those on the destination machine.

If you want to use AHCI mode, you will need to specify a third party storage driver for your machine at the start of Windows XP setup by pressing F6 when prompted. Personally, I stick to ATA or Legacy hard disk operation mode on all the workstations that I use FOG on (if they run Windows XP).