Summary
(So you don't have to read the 20 posts above)

My recommendation is the Optiplex 990 w/ Solid State Drives. These are prebuilt with Windows 7 Pro.

Give their sales division a call and see if they offer any volume discounts. You are buying 11 computers.

Get 64GB drives if you store data on the server. If not, get the 128GB Drives.

The reason I don't recommend configuring the SSD with Dell is because their 128GB SSD is pretty overpriced. ($314 dollars) You can buy 2 128GB Crucial M4s for the same price. Or get 3 64GB Drives at the current price. (Newegg just had a sale on these last week. $64 for the 64GB model, $128 for for 128 model, I bought 2 64GBs smile ) If you do end up deploying an image (strongly recommended for 11 computers or else you'll waste a week setting them up), they will get erased anyways so no point in buying from Dell.

Specification and Links:
Optiplex 990 - $754 w/ 250 GB Drive Desktop Slim
Dell Optiplex 990 <- Click Here for Preconfigured Desktop
[Linked Image from ]

-Add 100 for 64GB SSD

Video of an Optiplex 990 with SSD: http://www.youtube.com/watch?v=OKXCOJ32Zec