Is your Civil 3D 2007 crashing every time you save or the program does an autosave? This is apparently a major headache over on the Autodesk newsgroups, and there is a workaround.
Here’s what to do: Open your drawing template (.DWT) file. At the command prompt, type PROXYGRAPHICS and hit enter. Next, type 0 and then hit enter again. Now, save your template file. Oh, and do this for any and all template files you may have.