MS Server 2008 R2 Minimums

Check below article

http://www.msexchange.org/articles-tutorials/exchange-server-2007/planning-architecture/exchange-2007-sizing-cheat-sheet.html

Sorry, I should have specified Exchange 2010.  

I have the processor and memory specs from MS, but I was curious as to what everyone else is deploying as far as base Hard Drive space for the VM itself.  For the Mailbox roles we are adding separate DB LUNs to cover all the mailbox DB space.  I just need the bare minimum for upgrades, the applications, patches, etc. Or essentially a feel for what everyone is deploying and is what is practical.  If I can get away with 40GB initially, that would be great.  We're looking for a small footprint on 6 servers.

I don't think you need 40GB for HUB/CAS role. For MB role also there is a calculator from MS. You can give the inputs and it will give you the result.

http://www.howexchangeworks.com/2009/11/exchange-2010-storage-calculator.html

I'm hoping that 40-45GB will work for what we have since we're tight on space right now.  My goal is to be able to create at least one DAG and it's going to be tight considering the size of our organization.  With smaller footprints initially, I may be able to create a DAG for redundancy and upgrade with more HDD space in the SAN later just in case we need to grow the size of the VM or the data drive (d:).

You can use dynamic VHD or whatever VMware calls it when you thin provision the drive. That will save you on SAN space now and in the future. I always thin provision my OS volumes. No need to tie up 60% of my space that will never get written to.