i guess its easy.
u can change the contents of different frames from any frame using parent.frames[1], etc.
suppose u have 2 frames, they get numbered as frames[0] and frames[1]. assume u call the form in one frame as 'frm'. now in the onclick event of the other frame where the submit button is, put this code:
<input type=submit onclick='parent.frames[1].document.frm.submit()'>
this should do the trick. (may b i made some small mistake, but just fool around with parent.frames[] and u'll get it).
luv
Karthik.