Yup...check
VNC. But why in the name of all holy deities would you want to use a cruddy Win98 box as router/server??!
Wouldn't you be better of using a prebuilt/out of the box linux or bsd router solution? More stable, helluva lot more secure...
BTW. VNC isn't secure by itself, but you can make it secure by using an SSH remote shell server on your routerbox. That would also make secure/encrypted connections to your WinXP box possible (even though it's behind a router, SSH does TCP/IP tunneling).