I'm not familiar with either of those states. You may want to wait until someone familiar with them replies. Try changing the your subject (i.e. "Re: Moved IA to MO. Not splitting state tax correctly").
That said, this usually works:
At the w-2 screen split the boxes 15-20 W-2 info into 2 lines. On the 1st line leave IA in box 15 but make box 16 the amount you earned prior to the move; leave the IA withholding in box 17. On the 2nd line put MO in box 15 and the MO wages (after the move) amount in box 16; leave box 17 blank. You will probably have to attach a statement to both returns explaining the situation. Be sure you file a part year resident retun for each state.
