Do you mean to run opposite Vista? As in a dual boot? Is the hard drive with XP on available to the new computer?
If so, when you get the new PC put the XP hard drive in, then use your XP disk to repair the XP install so that the kernel will work with your new hardware. IF YOU YOU JUST REPAIR IT WILL NOT DELETE ANY OF YOUR FILES. Then use your Vista disk to repair the bootloader so you have the option of booting to both.
If you just want all your stuff on Vista use the Windows Easy Transfer feature.
When you come to actually doing this, let us know which method you want and we can make a detailed step by step for you
crabby