Yurii Rasskazov has written a great blog on his experience setting up VSS with Dynamics AX. Here it is:

http://axaptabuilder.blogspot.com/2006/06/notes-about-my-experience-in-setup-of.html

For more information on the version control system in Dynamics AX see the topics in the Microsoft Dynamics AX SDK under Microsoft Dynamics AX Programming Environment / MorphX Development Tools / Version Control System.