I disabled Data Execution Prevention (DEP) and was able to play for several hours without a crash for the first time since 1.1 was released...
I don't think leaving DEP disabled is a good idea but in the short term it seems to have a made a difference for me at least.
EDIT: 2nd kerbal session and still no ntdll.dll crash ... here's how to disable it manually and the program I downloaded to do it for me:
How to completely disable DEP
How to disable DEP for a single program
Tool I used automatically disable DEP