Depends on what exactly your serving is doing?
 
You wouldnt be running a "regular" edition of NAV on an exchange server.
 
I go with TrendMicro, Sybari, and Command.
 
My $0.02

i use norton 2003 to all istallations but if you have workgroup\domain i think that norton corporate 8 is better.(if you have money to pay)

Either Norton or Trend. TrendMicro is a little easier on the system and there is a good chance that you'll have it on your mainboard's Driver Disk.

Norton is the BIGGEST resource hog in the industry. It puts itself in the boot lineup, causes the most install problems with other software and weights the system down.
 
Go with System Suite from vCom and the TrendMicro AV. It has free updates unlike Norton who charges you!

Oh please.
I have Norton 2003 running on my home machine.
It loads with Windows and I have it set for full security, ie all files are scanned before execution.
All e-mail messages are scanned as they arrive and as they leave my system.
The impact on system resources is next to nothing and with a real-time scanner running you are not going to get infected with anything.
The corporate edition we have running at work also does real-time scanning and checks all e-mails and as I type this all of the services used by the program take up no more than around 12MB - there is also no drop in performance because it is running.