Unexpected Bizarre Behavior on Windows Network

I have 2 WinXP Pro (SP3) computers and a Win7 Ultimate
networked together at home. They were all living happily together
with printer and file sharing and shared internet until one of the XP
computers had some kind of serious virus invasion. After some
struggling, including at boot and scan with an Avira Rescue Disk, this
one computer was no longer able to connect with the other computers,
in fact it didn't see the networked computers or the workigroup. Oddly
it still has the internet connection and will connect to another
computer with Remote Desktop Connection. This is a nuisance
especially because I backup the computers on one another and transfer
a lot of files back and forth when I need storage space.
Any ideas?