keypress style for alphanumeric textbox help plz.

Question

hi,
i am very very new to C# and although i am used to VB 6 and a bit of C++ and JAVA.. i cant seem to find how to control the inputs on a text field.
i need a filter for my textbox that only accepts alpha numeric input.
i was thinking over the line of  having a keypress event and checking at textbox_change that each char is alphanumeric. how to do this. plz can anyone give me a skeleton or the textbox_TextChanged function!?
I am using Framework 1.1 i think thats why i dont even have the maskedtextbox commponent to help me :-P..
plz reply asap!
thanks...