However, there is another windows 98 computer which is cross-cabled to the other 98 machine which wouldn't accept a wireless pci card (2 different cards both of which worked in the other 98) in any of its slots, so I connected it to the router via a cat5 cable to access the internet to no avail.
This machine therefore has 2 network cards but can only find the other 98, whereas the the other connected to the router wirelessly can see all three computers and access the internet.
What needs to be done? Is the cross-cable interfering?