It's not official quite yet, but you can go ahead and start learning ASP.NET 2.0 from the experts at the ASP.NET 2.0 Quickstarts site: http://beta.asp.net/QUICKSTART/aspnet/.

I've been told that they may be making tweaks between now and the official Beta 2 release, but don't let that stop you.  There's a lot of good content there!