Extending the functionality of CMD.EXE

I would like to add some useful features to the command prompt inside of WinNT. I've sorta written my own win32 console app which does some of the functionality of the cmd.exe, but it doesn't do the full job. Is there any way to hook into cmd.exe or is the source to it released somewhere on the net?

One thing I would like to add is a TAB completion for directory / file names. I know that the cmd.exe already supports this, but I would like to have the feature implemented differently.

Thanks...

Rick