The main AV for Linux is Clam or Klam (KDE) although I have found it to be poor.
AVG makes an antivirus programme for Linux. There is also Avast, Aegis, Panda
and F-Prot and a few commercial ones such as Avira, Kaspersky and Vexira Central
Command.
See: www.linuxsoft.cz/en/sw_list.php?id_kategory=49

The problem is that with any I have used you have to manually scan everything.
You can run it on whole computers or folders, but it does not scan incoming
files. You need to install Dazuko to do it in real time and it is a real
nuisance to set up and IMO not worth the effort.

There are several distros specifically made to clean Windows viruses. Most use
F-Prot. The are Live CDs. I like Helix which is based on Ubuntu. See:
http://lwn.net/Distributions/#secure

To protect a network, try Untangle.