Time is running out on Windows XP

Everyone knew that it would eventually happen, however for those of us that are purchasing Windows XP Professional licenses to run XP based virtual machines, this is a significant moment.  After 6/30/2008, many distributors will no longer be selling Windows XP Professional.  So if you are planning a VDI deployment using Windows XP Professional, you may want to get your OS licenses ahead of time, other wise you are stuck with Vista.  I do believe you can downgrade a Vista license to XP, but I am not totally sure of the process or if its actually possible.  I also don't know if this affects Volume Licensing customers as well.