Do you have all your machines in the same workgroup? To find out on win98se just go to:
start\settings\controll panel\network then the identification tab.
there should be a box that says "workgroup".
For windows XP professional go to start\settings\controll pannel\sysytem properties
and then the "computer name" tab. It should list the workgroup your in. Make sure that all the machines you want to network are in THE SAME workgroup. If you need to change the workgroup in XP then just hit the "change" button on that same screen you were at that shows the workgroup your in.