there are ways to get onto a plain win98 comp.
there have always been problems with ms's security management and especially the sharing setup..
.. but if you want to have full access and control you certainly need to install a trojan like sub7.

i would say the easiest way to solve your "problem" is to get into onto a shared device (you need to have access to the startup-folder); upload a trojan-server; and let the computer crash down, on the next restart (computer must start normally) server installs automatically and you have your full access..

..this is just one way of doing it.. greets