Trend Micro's Worry Free Business Security 5.1 (soon to be version 6) is a great replacement, in my opinion.
It is loaded on the server, licensed and administered centrally. The administration console runs from Internet Explorer (ActiveX controls), so any computer able to access the server via TCP can be used to launch the console.
It will use an existing mail server to drop reports and alarms, with a small amount of adjustability in threshold levels.
I also have had to clean up after multiple Symantec explosions, and a few Trend Micro explosions, and Trend Micro is by FAR the easiest to tame. Symantec can easily take an hour to clean out the registry. I've even been able to recover a TM installation that crashed (thick dust bunny lodged in CPU fan creating thermal event), just by starting the install again, uninstalling, then reinstalling. Symantec would have been a nightmare...
Trend Micro also offers hosted email solutions, in addition to their product that sits on an Exchange Box (WFBS Advanced), though my experience is all with the latter.
Decent spam detection/removal, excellent virus detection/removal, and better prevention of trojans when the Reputation Service is used (browser URL monitor).
It will work with an existing IIS installation or install Apache, if need be.