The interface to the new tk_messageBox is exactly the same as the original. You should be able to drop this new module into your existing Tcl/Tk programs without having to change a thing. The code is in a file named msgbox.tcl. Just download it and make is a part of your program, or use it to replace the "msgbox.tcl" file in the standard TCL library (usually located at /usr/local/lib/tk8.X or /usr/lib/tk8.X).
The following table shows a comparison of the old and the new tk_messageBox widgets:
More Tcl/Tk Widgets