First, do not delete anything on the W98 system. It will be your "backup" in case you need to fall back and try again. Hopefully, she has been backing up that data to floppies, Zips, CDs, tapes, or something. If not, you should highly recommend that she does so once you get it moved to the XP system.
What DOS program is it? Sounds like it could be an old data base program.
Is it running in a Win 98 window, or does it run only when she exits to DOS?
Many old DOS programs need certain parameters that are set in either the "autoexec.bat" file or the "config.sys" file when the system boots up, so you may need copies of both of them.
Give us more information and we may be able to give you enough guidance to get it working.
to the board, Vicman.
Doh, where are my manners?