What would be my best option for Antivirus/security on a 10 workstation network running Server 2k3 r2 sp2 64bit

Here is a good link you may find useful. There is also a free trial available on their site I would recommend trying.

http://www.symantec.com/business/products/purchasing.jsp?pcid=pcat_security&pvid=endpt_prot_1&om_sem_cid=biz_sem_nam_us_Google_SMB_Store_SEP&mktsrc=paidsearch&om_sem_kw=symantec+endpoint+protection

If all of your systems are in the same location, I would not go for a 'managed' solution. The additional expense will be substantial.

MSE will be free for your number of seats - and you can add another layer of security with Malwarebytes (Pro) for about US$20/each.

Add in a good hardware firewall and you will have even more protection.

This EE Article was written for home users, but all of the advice applies:
MALWARE - "An Ounce of Prevention..."

I do have a Firebox hardware firewall, and am running MS Exchange... One thing I forgot to mention in the intro is that we may be implementing Sharepoint in some capacity or other over the course of this coming year. The other comment I have is that I am a part(sometimes very part) time network admin, so anything that justifiably automates my job is worth the investment... having said that, if installing unmanaged solution is substantially cheaper and does a better job, I would definitely be interested in looking into it. The related question ... would the same software installed on the workstation be able to be used on the server?

Not sure if I need to post a new thread for this, but I was also looking into Invincea browser protection... has anyone had experience with that product yet? I contacted them, and it sounds like the commercial version will only be available 2012 Q2...It is currently targeted at large corporations and govt entities...

Given that you are running exchange you might wish to look into Microsoft Forefront Endpoint Protection.  I don't know much about it other than after much research and consultant input our network department chose this as the solution they are going to use after everyone is migrated over to exchange (almost done).  Currently we use Symantec endpoint protection (and you need the server version of this if you intend to run on servers) and I have found it to be undesirable (personal preference and too much of a hit on system resources).

I appreciate all of your input...I am not ready to make a decision immediately, but your input will definitely carry a lot of weight in making that decision. Will try to distribute the points as equitably as possible.