[2005] Voice Command (Not T-T-S)

Hello, i was searching on the internet and all i found was T-T-S (Text-To-Speech). I know how to do T-T-S, but what i want to know is how to make my program reconize certain command. I want it so (as an example) when the user says into his/her mic. "hello" a message box will be displayed with the text 123. How is this done? What reference(s) do i need? I already have on the program all the references i could find relate to speech..i think at least. Though i don't know which one to use and how to use it to understand the user.