We installed .net 3.5 beta 2 on a web server this morning. It did not work. Even our 2.0 webs stopped working. So to save others the trouble...
Go ahead to
Go ahead and remove all instances of xmlns="" and you're good to go!
Also worth mentioning, 3.5 and 3.0 does not appear in the ASP.NET tag on IIS, only 2.0 does. This is because 3.0 and 3.5 are extensions of the 2.0 framework.