There's a whole bunch of ways of doing it, but the fact that you are asking the question suggests you are not a network wizard, so a free utility download here is probably your best bet
That should let you do a remoted close down. If you want to go a little further, and remotely manage the Xp desktop from the 98SE machine, as though you were actually sitting in front of the Xp machine, then there is a very good little opensource utility at www.realvnc.com.
Download and install on both machines. Run the service mode 'start service' on the XP machine. Run the viewer on the SE machine and enter the IP address of the XP machinem then you can see your XP desktop from a browser in your SE desktop. That pretty much all there is to it. Easy to install and use, but the documentation is not easy to find.