Direct Cable Connection (A Windows tool, see the HELP files for setup) will work if both computers are using the same OS, but if you try XP/98 it might not work. I tried and could not connect an XP machine to a W98 but it is fiddly and needs to be set up just right, so it could have been my fault. You will also need a special cable to connect the two, and XP only uses a Serial cable, while 98 can do it with a Parallel cable or Serial. When it works it is a good way to read the other machines files (file sharing allowed of course) and to transfer data, although it is not fast.
I apologise if I am telling you how to suck eggs.