You mentioned the big three, Trend, McAfee and Symantec, and while other companies have useful antivirus products, these are the most popular choices, with Zone Labs and F-Secure often included. All of this software will do what you need -- protect your PC, inform you when you are being hit, provide several levels of manual or automatic intervention, offer an easy push to the desktop and painless frequent signature updating.
Personally, I've found that Symantec's Anti-Virus Corporate and Enterprise Editions are very easy to administer at customer sites that don't have a full-time support staff, and integrate well with W2K3. My next choice would be McAfee, as they have a lot of experience in integrating antivirus software with the enterprise.
A great site that allows you to compare the major antivirus software vendors is Top Ten Reviews. They just released their Antivirus Software Review of 2007.
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