I'm not familiar with BootMagic, but I might be able to help you out anyway. Assuming that you have the original install disk for BootMagic, try this:
Check the documentation that came with BM. It may tell you how to proceed. You may be able to simply boot into Win98, insert your XP CD, and install it, and be done, or you may have to install XP and then reinstall BM to regain your dual-boot capability. It is possible that you may have to uninstall BM first, then reinstall it afterwards, the BM documentation should tell you. In either event, I would recommend making a full backup of the entire system before you start, so you at least have a way to go back if something goes wrong.
If you don't have any documentation with BM, I'll recommend that you change to a different boot manager. I've got one here that I'll be happy to send you, or give you a link where you can download it. It makes such system changes simple. With the boot manager I use now, you simply install what ever you want, then reinstall the boot manager, and it picks right back up where it left off. In fact, it would make it really simple to install XP, while leaving everything already in existence exactly as-is, if thats what you want to do.
If you have the documentation with BootMagic, but still aren't sure how to proceed, send me a copy of the document ion, and I'll see if I can "interpret" for you.
