If [ Get ( LastMessageChoice ) = 1 ]
Else If [ Get ( LastMessageChoice ) = 2 ]
Do something else...
Just to mention a gotcha if you are wanting to write input data to a table ... only the default 'rightmost' (button 1) will do it so you should always make OK button 1 (if you want to write data on the OK).
Just to further clarify what LaRetta stated, when using the input fields in the custom dialog options, only button 1 will execute writing the data.