Please refer http://channel9.msdn.com/pdc2008/PC03/ for more detail.

API analysis:
Working machine and driver:
Summary:
Multiple touch depend on Target machine, OS and driver. Especially the driver and OS. Sometime we found the driver may failed after some instruction. It is greate for any app to support multiple-touch, but how to work-out a greate user behavior is harder than migration.
Reference: