Splitting up a sentence into different strings

Just like the title says i need to take a large string lets say like 200 characters long and split it into a bunch of strings that are 40 character in length.

Background: Think of a basic RPG game for gameboy and how when a is pressed a box pops up showing what they said. I have it all set up to show the message every time they hit a (space for me) all i need it to do is actually split the senctence into each part it shows.
THX, to whoever answers it.