Maccip,
Check out this discussion string . . .
http://discussion.autodesk.com/thread.jspa?messageID=5005214
It appears you can you the following software to convert the LD .lib files into a .net object model.
http://www.aurigma.com/Products/COMtoNET/
I haven't done a lot of programing with it but it appears to work well.
If you would like to collaborate on it or would like some actual sample codes email me at:
civil3d.net
gmail.com
Good luck,
Scott