Somewhat interesting PC setup problem

I have a super new monster toy to play with, and I'm looking for suggestions/discussion to consider for it's setup.

Here what it needs to do:
- multiple users with remote desktop connections (Initially 2-3, Max I think would be about 6)
- running long simulations/analysis of optimizations (Applications are all MS Windows based)
- Background MySQL and/or MS-SQL DB servers
- If possible it should be a part of our central AD domain. (For user auth and file share access, not required for base OS as there are other intricacies that makes this optional, but it would let me offload user account mgnt.)

But other than those constraints I'm open as to how I implement this on the new HW. So what would the other techies on my f-list recommend:
- Virtualization (Options include VMware Workstation, something I can download free from internet, or Windows Terminal Server)
- Base OS (Options include Windows [XP64, Vista64, Server2008x64], or Linux [RH5x64 prefered, but not mandatory])

Any other ideas I should consider?

What I'm leaning towards now is:
- Linux OS Base
- VMWare VM's Running Windows for:
-- DB's
-- Separate XP App machines (Each user gets their own VM to play in)