And here´s the solution:
I started Windows Update and installed KB951847 (some .NET update), then Restart, again Windows Update, two other .NET updates installed, again Restart and then open VS 2010 beta 2.
This time not VS started directly but the dialog where I can choose my environment (in this case I chose C#). This dialog didn´t appear before. Then VS started and I was able to create a new project!!
I started Windows Update and installed KB951847 (some .NET update), then Restart, again Windows Update, two other .NET updates installed, again Restart and then open VS 2010 beta 2.
This time not VS started directly but the dialog where I can choose my environment (in this case I chose C#). This dialog didn´t appear before. Then VS started and I was able to create a new project!!
At first reset your VS 2010 settings by calling "C:\Program Files\Microsoft Visual Studio 10.0\Common7\IDE\devenv.exe" /ResetSettings. Afterwards I resetted the settings via the menu (Tools -> Import and Export Settings -> Reset all settings -> C# Development). I remember, when I started VS 2010 the first time, I selected the option to use the settings from a previous version of VS (I've installed VS 2008 and VS 2010 in parallel).