Ok that makes this harder then, sec explorer is a tool which goes beyond the regular NTFS permissioning screen, not used it on win 7 before and not sure how that will transgress through from 7 to xp but it wont hurt from where you are now and shoudl allow you as long as logged on with admin to overwrite and force permissions down from root of drive
http://www.brothersoft.com/security-explorer-download-48280.htmlgive that a go and let me know how you get on, if that doesnt work there are other things that can be done but may require a data transfer kit