I agree to ibu1. As far as I am aware, Clamwin is the only free antivirus solution that you can install on Windows 2003 server. However, it does not offer real time protection and the scan rates are extremely slow.
If you take my advice, its much better to opt for a paid software for server security. Plenty of choices available: Eset Smart security business edition, Bitdefender Business security, Vipre Enterprise edition, Symantec Endpoint security, Mcafee Total security for endpoint and so on. So make a wise decision keeping your present circumstances into consideration.
Post back if in need of further assistance.
