Literally the day after I posted this, my server locked up again... I will post another update if I get it fixed!
I have been plagued with a very strange issue that I finally found a solution for. I had a Server 2008 R2 VM running Exchange 2007 that would just totally lock up randomly. The only way to get the box back was to do a reset from within the VM client. My client was running ESET Mail Security as the anti virus on the box. When I removed the anti virus the problem went away. This however, is not the final solution :)
It was extremely difficult to troubleshoot this issue since there were no crash logs at all to debug. I was desperately looking for some kind of a pattern to the crashes but I couldn't find anything consistent. There were no indications in the event log of any problems prior to the crash. I began disabling other agents running on the machine, updating VMware tools, installing the latest service packs etc. but nothing fixed it unless I removed ESET.
I found a post talking about a similar issue (with NO mention of ESET) that recommended increasing the Video Ram on the virtual machine. On this particular box, it was set to 8MB, I increased it to 64MB from the VM client. Since doing this, I have not had this box lock up in the last month. I also reinstalled ESET and everything is working perfectly.
What makes this issue even more bizarre is that I ran this particular server with ESET on it for 4 months prior to deployment and even had a few mailboxes running off of it and NEVER experienced the problem. I was fighting this isue on another Exchange box running Server 2008, not R2. I figured I would try a 2008 R2 box since I was literally out of other options. The problem came back after I got all these users over to the new Exchange server. It appears the issue only occurred for me when the Exchange server actually was servicing a number of mailboxes.
Hopefully this post helps someone else having the same problem.
If you're not sure where to do this, just edit the properties of your VM from within the client and modify the Video Card settings you see here. The VM has to be turned off before you can change this value.