keypress and tab key

i'm trayng to validate the contents of a combo box, before the user can change focus (could work easily doing it after, but i wan't to reuse some code)

the problem is that i'm tryng to watch when the tab key is pressed in the combo box, but keypress doesn't seem to work (nor does keydown or keyup)
any ideas why it doesn't work? any workaround?

(i do not whish to use the lost focus event since some of the code will apply to the "me.activecontrol" and when i tried this the activecontrol wasn't the combobox anymore)

thank you a lot!!!

Yo soy el que hace que llegue a ser