The most logical thing to do would be to catch this with the KeyPress event. There's a problem, though - the KeyPress event gets raised *before* the key you pressed actually gets added to the textbox. At least that's the behavior on my desktop and device.
So I've been using a little workaround that involves a timer. Create your form, textbox1, textbox2, and timer1.
You could use my ControlEvents library that adds "missing" events to B4PPC controls and catch the TextChanged event of the TextBox which occurs after the key press is added. Much better than cheesy hacks (Apologies willisgt!)
Sounds like you need to learn how to use libraries. You should have downloaded the latest ControlEvents version from either Post #5 (.Net 2.0) or #6 (.NET1.0) from that thread. One of those files is a help file, the chm, the library is the dll - stick the help and the library in the Anywhere Software Libraries folder. Ignore and discard the cs file - you don't need it.
Restart B4PPC - Desktop. The ControlEvents help should now show under Help - read it and the Main help about libraries.