Nework hell!

I recently setup an office network for a friend involving a Windows 98
computer, a Windows XP Pro computer and two Epson printers: an Epson
AcuLaser C900 (laser) and another model which I can't remember. Anyway when
I left a few weeks ago it was working fine. However they called me over the
other day to sort the mess out as for some reason (virus?) they are no
longer able to share files or printers or use either of the printers.

When I invesigated the XP Pro system had lost Administrative Control (I have
put that back after running a Windows Repair off the XP CD), but neither
system is able to see each other. I have insisted that these guys buy an an
up-to-date virus scanner and run that after running ad-aware and seeing how
much crap was in the registry. It incenses how people can let their
computers get in such as mess and then expect people like me to pick up the
pieces!

Anyway, how do I the two machines to see each other again? As I say, the
chances are, that some worm has got in there and wreaked damage, but surely
the system repair has solved a lot of the trouble. Both systems use the same
workgroup name. A Linksys - Cisco hub is being used.

Cheers in advance