The most useful thing I've ever found by accident

http://www.kbcafe.com/articles/HowTo.Shell.pdf

AND I QUOTE:

The next easy task in creating shell extensions, is add items to the context menu of file
types. A neat little trick is to add a shortcut to the command-line shell in the directory
context menu. This is done by making a small change in the Windows Registry. Simply
add a new subkey in HKEY_CLASSES_ROOT\Directory\shell. Here's .REG file that
adds a CmdHere item to the context menu for folders.
REGEDIT4
[HKEY_CLASSES_ROOT\Directory\shell\CmdHere]
@="CMD &Prompt Here"
[HKEY_CLASSES_ROOT\Directory\shell\CmdHere\command]
@="C:\\WINNT\\System32\\cmd.exe /k cd \"%1\""