Free antivirus program for Windows Server 2008?

I tried to install the free version of Avast on windows server 2008, but it says it’s not supported. The server version of avast has no free version. I have norton 360 that I could install (from a box with 3 computers supported) but I was kindof hoping to sell it to get some cash. Is there a free antivirus that will work well, or should I just throw norton in there?