I don't know if there is free software that can do it but PowerQest's
Partition Magic can do it and you won't need to reformat. www.powerquest.com, note, check the site for versions compatible with XP.
Try using Partition Magic's emergency boot disks, that way you'd be
accessing the options from outside XP as that might make a difference.
Also, be sure your version of Partition Magic is compatible with XP.