Kevin,
I looked at the file you referenced and though it mostly works it still has some major problems. I posted this in your section by mistake - this is a general .NET problem. After looking at the code sample we have some ideals about how to do this efficiently, so that we can provide an input mask like VFP's and make the subclassed input box work like VFPs. Oh joy, I will be able to type in numbers correctly again !!!
A problem is a problem only as long as it has a possible solution. Lacking that, it becomes a FACT!