this is a very good trick ritesh,especially the first one...
but i am telling you the real thing that is happened...
you have changed here not the functionality of "ctrl+alt+del"
but the functionality of "task manager"..
try to open task manager in any way after using this registry hack..
you will also find the calculater as your friend..
you can use any ".exe" file in place of "calc" ..
this will open the specified exe program that you have used in the value of debugger...
you can use this trick with any program like wmplayer.exe in place of taskmgr.exe
just make a key under "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Image File Execution Options" with the name of exe file for eg.wmplayer.exe and create a string value in right pane,name it debugger and put the value to the path of exe program that you want to execute in place of real program..for eg. notepad.exe
and change the functionality ....
try it, i am sure,you will enjoy it..