I'd start by getting a brand new PCI network card for the desktop. That'd beat the dongle in speed anyway, and cost only around 6 GBP apiece (my foreign estimate).
Then, I'd remove all the network adapters from the Control Panel, reboot, and let everything reinstall itself. (Make sure you get the 98 drivers on a floppy for the network adapter). Your old MS network may then require reconfiguring, so make note of the PC and Workgroup names if you used a non-default value.
