I've got an external USB LiteOn DVD-RW drive hooked up to the Mini through an IOGear 7 port powered USB hub. It works fine.
I installed XCode, X11 and some other goodies for some future experiments from the Admin Tools Install CD.
But, there's no obvious way to install Rosetta. There are lots of pointers out there that indicate either: 1) You can install it from the Snow Leopard Install DVD, or 2) The OS will throw up a popup window and offer to download it if you have an application that needs it. Neither were happening for me - Rosetta isn't on the OS Install DVD in an obvious way.
Turns out, Snow Leopard Server is different.
http://support.apple.com/kb/HT3877
Gotta use the Terminal. (Here's hoping that set of instructions still works...)
More later, it I get it to work...
Cheers,
Scott.