A few years ago I plunked down $1200 for 20 nodes/2year licence of McAfee Anti Virus Suite, which includes a monitoring/policy enforcement suite that's run on a separate server. It is the best investment I've made to date. Update files are pushed to me weekly (or sooner if there's a real baddie). It can be set up to notify other people/machines/pagers 12 ways till Sunday. The only tweak I had to do was run a registry mod (we're a Win2k shop) to limit processor use during the daily 'full machine' scans that I've required for everyone. In three years (yes, I renewed the lic's) I've not lost one file due to virus, despite hundreds of hits from every concievable source. I highly recommend it (and no, I don't work for McAfee).

-Zeke