If it gets done under FDISK, it will kill everything on the hard drive, unless there just happens to be some unpatitioned space. But, these days everyone uses the entire disk for Windows. So, I'd be shocked to see an undefined space on a disk.
I'm not sure how XP works with something like Partition Magic. If one were going to take that route, they might as well make it a DOS partition. Of course, one would have to have a copy of some verion of DOS to make it work. I've got 'em back to someting like 2.11 all the way to 6.x.