We're building an automated QA enviroment for our dev team using SCVMM and I was wondering if there's an easy way to add guest machines to AD from SCVMM.
Yes its possible to do this, using a syspreped image, something that you can create without SCVMM if you use SysPrep. Information on SysPrep can be found here: http://technet.microsoft.com/en-us/library/bb457073.aspx (This is XP specific but there are articles for Win7).
SCVMM makes it easier to prepare your image, as you can image a VHD from within the software as outlined in the following technet article: http://technet.microsoft.com/en-us/library/cc956136.aspx
Creating the Virtual Machine from a template is outlined here: http://technet.microsoft.com/en-us/library/cc764306.aspx pay attention to the section on the answer file which is how you will auto join your VM to the domain.