When I am rendering an animation, even a little one (60 frames), the program suddenly close without any notice. I tried AVI, Quicktime and DivX codecs, and the same thing occurs. My computer: AMD 1.2Ghz, 256MB RAM, 20GB HD - Windows XP. Note: I use 3D studio Max with no problem.
Which version are you using? If it's Version 2 check to see that Autosave is turned off. There seems to be a bug that often causes c* to crash when autosave kicks in during rendering or Ram caching. I had the same problem and this sorted it out.