I've decided to change the HAL type once in the OS using a VBScript. It's not quite as nice, but it works for me very well. It changes the HAL by modifying the boot.ini to include /kernel=ntkrnlmp.exe /hal=halmacpi.dll. Basically, it gets the processor name, and compares it against a list of processors that I put in at the top of the VBScript in an array. I only really enable the MP HAL if the computer is a dual core computer, otherwise, ACPI works for pretty much everything else just fine. I've done some speed tests, and haven't found any issue in running with the ACPI HAL versus the ACPI Uni HAL.