Cut off where? Do you want it to sit over the top of the white image to the left? if so, add this:
background: url("../images/shadow.png") repeat-x scroll 0 0 transparent;
margin: 0 0 -120px;
<font color='"#FF0000"'>position: relative;
If that's not what you mean, what browser are you using?
EDIT: the code above isn't workable, I now realize, as it makes the form unclickable, so please ignore it.