Upgraded 98 to XP-Pro, Need login help!

Had a 98 box, standalone, was once connected to some LAN for transferring data, but later out of domain.
Recently upgraded it to XP-Pro, dint know there was a default ‘Admininstrator’ user in it. After installation is complete, it is prompting me to provide an administrator password!! I dont have any!!! How to workaround this?? I have a lot of data on this pc, please help.