Did you install the latest service packs? I've had it working for the past year on x64 Pro (i know, i know, whoop-de-doo), but of course I forgot what I had to do to get it there (I had the same errors)... Download and install the latest versions of the .net packages from Microsoft (1.1 and 2.0). Uninstall and reinstall Civil 3D and see what happens. I dont think I got everything to work correctly until I installed SP2. (SP3 works great also)
Before you go through all that, go to options > files > support file search path - change all the paths by clicking browse, then go to C:\Program Files (x86)\Autodesk Civil 3D 2007\ (or wherever you put the default install folder) and click the appropriate file...this will be the same path as before, but some folders may be capitalized...for some reason i did this with vista x64 before and it got a few things to load. Let me know how you make out...