You can do remote assistance as the helper if you have the Remote Desktop Client (and the helped person is on XP)
http://www.microsoft.com/windowsxp/d...dclientdl.mspx
You can't be the server (the person who needs help) from Windows 98 though.
The alternative is to use VNC. There's many versions out there, but the most basic flavor is RealVNC. Just get the free version
http://www.realvnc.com
It's very easy to setup, but you need decent bandwidth to run, and you need to know your own IP address (you may need workarounds if you're behind a router or a firewall).
The person helping you via VNC doesn't even need the client (though they can download VNC and run it if they want - it works a tad better). All they need is a java-enabled browser (get java from java.com if needed). Then in the URL bar they type your IP address followed by a colon, then 5900 (that's the port where the java/browser server listens). For example
http://1.2.3.4:5900
Tips: if you're low on bandwidth (dial-up) try using less colors (even 4 colors is enough if you're doing basic work).