If you have 2013 installed and are thinking of installing the .NET framework 4.5 preview ; don't.
Simarly, if you have 4.5 installed don't bother installing 2013.
There is a compatibility issue between the 2.
AutoDesk are working on a resolution.
Uninstall 4.5 and reinstall .NET 4.0 in order for AutoCAD 2013 to run.
Regards
Kerry.
added:
One of the benefits of sending Customer Error Reporting (CER's) is that sometime the problem gets solved.
Symptoms.
Crashing on closing ( reproducible )
Crashing on some Dialog use. ( reproducible )
Crashing after a sequence of commands.