While you may be running your server OS as a workstation, the server product allows for more plugins. Such as Exchange, Sharepoint, ISA protection, etc... You can't run these programs under a desktop O/S, so there is a seperate product (Avast! Server) that covers these programs.
However, I have installed a standard professional edition using ADNM on a windows 2000 advanced server that is ONLY used as a print server with no problems. I fear that I may be violating the license terms using the product in this way, but have yet to look into it.
