Since the BDD 2007 timeframe there has been an issue in BDD/MDT when doing a build and capture of Windows XP/2003. Sometimes the Task Sequence / Sysprep just hangs, until you move the mouse. Here is the fix.
Note: This only happens when building reference images of Windows XP or Windows Server 2003.
Overview:
The solution to the problem is to run an AutoIT script that automatically moves the mouse every now and then. It needs to be run as an exe, but I provide the AutoIT source code so you can see what the files does. Just call the .exe file before the Sysprep action in the task sequence.

/ Johan
Note: The script originally came from the Deployment Fundamentals – Volume 3 book (written by me, Chris Nackers and Mikael Nyström).
Here is a little more on the subject that someone else posted concerning CItrix/XenApp and the Hang: blog.stealthpuppy.com/virtualisation/automated-citrix-receiver-deployment-hangs-indefinitely/
Great, thanks Jason
/ Johan
We actually have found that this happens on Server 2008 R2 as well, using SCCM/MDT when installing XenApp 6.5 software. It pauses the whole process (indefinitely) until the mouse is moved within the VM. This scripted works well in both cases, thx Johan. 😉