An alternative to consider is Microsoft's new and FREE antivirus ( http://www.microsoft.com/Security_Essentials/ ).

If you decide to give it a try by all means tweak/configure it ("Settings" tab of the application) otherwise it considerably slows down the workstation. The key is to define which processes, files types and locations can be excluded from its real-time scanning making sure to include DBFs, CDXs, your own EXEs and other safe items.