I do an aweful lot of consulting for small businesses. And I use Kaspersky Business Space security.
nod32 and kaspersky have similar performance impact (much less than most... including symantec and mcafee) and similar success rates at catching viruses (again, much better than symantec and mcafee)
Both nod32 and kaspersky have administrative consoles that manage the network via a server (think policies, update distribution.)
Why do I generally recommend kaspersky.... it's a couple hundred dollars cheaper....
One little hint. If you run a linux server, most admin servers run only on windows (using msde sql server junk.) Not a big deal if you just load up vmware/xen/whatever. A small windows partition solves this problem without jumping though huge hoops.
Oh, and the stay-away froms....... avg, ca (never catches stuff), symantec (tends to hose up the system) .... this is just from a tech that has fixed a couple hundred computers with those installed.