SCVMM 2012 SP1: P2V of XP SP3 is not supported
Have you tried to convert XP SP3 machines with VMM 2012 SP1. Well, per TechNet, P2V Prerequisites, P2V of XP SP3 machines is not supported with VMM 2012 SP1 (you need to have pre-SP1 VMM). If you have visited this page earlier, be warned that the page was updated on March, 13th.
If you come across a situation where you need to P2V XP SP3 and have VMM 2012 SP1, your first bet (free alternative) would be disk2vhd from Sysinternals.
If you try it, first, for the boot volume you are converting, don’t forget to check “Prepare for use in Virtual PC”:
Second, after the PC gets converted, you will have to options to boot from: disk2vhd XP, and XP. I was able to boot from both but when disk2vhd is selected, I could not upgrade the HAL, it was getting back to HAL upgrade upon reboot. If you check the boot.ini, you will see halacpi.dll was added by disk2vhd for the default boot option.
In my case, I basically deleted this entry after ensuring that I can boot using the second boot option (noexecute and fastdetect) to make it default, then I was able to upgrade the HAL and install Integration services.
For more information about HAL options: http://support.microsoft.com/kb/309283