Antivirus Help

Hey fellow CAGs, I have a bit of a computer problem here. I want to install an antivirus program onto my computer. I am running Microsoft Windows Server 2003 Enterprise Edition on my PC. The thing is, I have Norton Antivirus 2003 and 2004, but when I try to install them, they say that they will work only on workstation operating systems, not server ones. Does anyone have or know of any alternative good antivirus programs that will work with my operating system? Thanks.

AVG used to be a good free alternitive for server software but they stoped supporting it and now you have to pay in their most recent version 7.0...if anybody else has any ideas I would like to hear them as well