A bigger issue to making a SQL Server a DC is the permissions that get set. I once (accidently) started to promote a SQL Server to be a DC (it was late, I was RDPed into the wrong server, I was young and naive!) It broke the SQL Server even after I cancelled the dcpromo...
I managed to get it back up and running, but it wasn't a fun time.
DON'T DO IT!
Take Elliotts' suggestion, find a decently powered desktop PC, load Server 200X on it and make it a DC. Or if you've got a virtualization environment (Hyper-V, VMWare) load a virtual machine and set it up as a DC.