Winternals ERD2005 is a great tool, but not cheap
Good suggestion, but BartPE is a free utility. Winternals ERD2005 is a component of the Winternals AdminPak, which costs over $1,000, unless you buy a volume license for your entire IT group. The Winternals Utilities include some essential tools that have saved thousands of dollars for my clients (and recovered data from dead hard disks that would otherwise be considered lost forever), so it was well worth the investment, but if all you need is a bootable XP environment, this works fine, and costs you nothing more than your own time.
I have also had great success with several of the free Linux bootable utilities (Knoppix, GPartEd, Ubuntu Live, etc.) which permit access to NTFS partitions from a Linux command line or GUI when XP just won't boot normally.