Via code: use SendKeys to send F4 to combobox
I'd like to do it via code but I have been avoiding SendKeys since I've heard it might cause problems with Vista (I'm using XP to develop the program) but your solution should do the trick. I'll have to do some more research about using SendKeys in programs that will run on Vista and Win7.

Thanks for all repiles; I will try them all and see what works.