Check out the post titled Bill Gates talks about Free Software, Students, and Technology for all the details including who is eligible and in which countries it is available.
There is a full list of products here which at the time I wrote this post were as follows:
Visual Studio 2008 Professional Edition
Windows Server 2008 Standard Edition
SQL Server 2005 Developer Edition
Microsoft Expression Studio
XNA Game Studo 2.0
XNA Creators Club Online