Some questions about Domains and Workgroups

Hi everyone,
I recently have had the task of rebuilding a small network and I had a experienced home server expert help me out for a few days.
What he suggested was that instead of having a domain controller and active directory like I originally planned he suggested that I just stick to a workgroup as it's much simpler.

There are two cons with that and one is the managing of shared folders.
Second is complexity of having to make dual accounts for mail and server access.

My setup will be about 20 computers running Windows Server 2003 and Kerio Mail Server. I choose Kerio because Exchange would have been much too expensive to run.

Anyhow my questions is, are there any major security vulnerabilities to a domain? Is a domain safer than a simple workgroup? Any comments would be appreciated. Thanks!

If you are not a full time administrator of the network, you're better off using the server as a file sharing system and setting up the dual accounts.

Its not an easy task to go in and create a domain. At about 15-20 computers you really should look at a domain but if you're not on it full time.

Unless you know how to setup a domain, don't do it in this situation. I'm a huge fan of domains but you're getting yourself into a big support headache.

But if you're comfortable doing AD and a domain, do it. If this if your first time, hold off.