Ctrl2cap is a kernel-mode device driver that filters the system's keyboard class driver in order to convert caps-lock characters into control characters. People like myself [Russinovich] that migrated to NT from UNIX are used to having the control key located where the caps-lock key is on the standard PC keyboard, so a utility like this is essential for our [Russinovich] editing well-being.
The primary purpose of this driver is not serve as a caps-lock to control mapping utility, but rather to demonstrate how system keyboard input can be caught and manipulated before NT even "sees" it. At this level it is even possible to filter out the ctrl-alt-del combination
Ctrlcap is actually quite trivial. It simply attaches itself to the keyboard class driver so that it will catch keyboard read requests. For each request, it posts an I/O completion callback, at which point it takes a peek at the scancode that is being returned. If it happens to be a caps-lock, ctrl2cap changes it into a left-control.
For a more general approach, see Changing NT and Win2K Keymaps through the Registry .