guys,
he is new at programing and your "throwing" all this code.... im sure he wants it simple
ofcourse that "simple" depends on preseption
in any case, here is simple (yet primitive) way for you...

mainstring :04072009

the input is a string , which means you can access each char (cell) individually
so...if you want to get the "4" then you can write mainstring(2) , cell number 2.

as for your example :
startMonth = mainstring(1) & mainstring(2)
startDay = mainstring(3) & mainstring(4)
startYear = mainstring(5) & mainstring(6) & mainstring(7) & mainstring(8)

by the way, & is appending (adding) to the end of the string