Re: Need help purchasing/creating a small desktop
Newegg.com is a good place to find all the components you need to complete the final assembly of a current barebones Shuttle system. My Shuttle, a model SN68GS has been chugging along on Ubuntu beginning with version 7.10 through 9.10. I have never had any problems with it since I assembled it three years ago. Try this link for a Shuttle that appears to meet your desired specs.
I've considered the shuttle PCs, but can't find good information about how Ubuntu-compabile they are.
All you need to do is add a CPU, memory, hard drive, and CD/DVD reader. Once you gather all of your peripherals, you can complete final assembly in a couple of hours followed by installing Ubuntu in less than an hour. It should work great.
System76 Pangolin Performance - panp9
Intel Core i5-3210M Processor (2.50GHz)-8GB DDR3
Intel HD Graphics 4000 - 250GB SSD