To find out more details about the Windows Phone 7 Developer Tools: http://www.microsoft.com/express/phone/. 

Windows Phone Developer Tools includes:

• Visual Studio 2010 Express for Windows Phone
• Windows Phone Emulator
• Silverlight for Windows Phone
• XNA Game Studio 4.0 CTP

A few good resources:

• Windows Phone Developer Portal
• Getting Started Guide for Developing for Windows Phone
• Code Samples for Windows Phone
• Windows Phone 7 Developer Training Kit