Your official information source from the .NET Web Development and Tools group at Microsoft.
If you haven’t installed the Visual Studio Mobile tools for building Win7 applications I would highly recommend you do so now via one of the following links:
The release notes can be found here: Release Notes
Programming Resources: http://charlespetzold.com/phone/index.html
Channel 9 Training: http://channel9.msdn.com/learn/courses/WP7TrainingKit/
Windows Phone Developer Forums: http://social.msdn.microsoft.com/Forums/en-US/windowsphone7series
XNA Creators Club: http://creators.xna.com/en-US/
Pre-Requites: Uninstall any non-RTM versions of VS 2010.