First, I'd try including all three sections in the form tag, ex:
HTML Code:
<form>
<div id="top"></div>
<div id="middle"></div>
<div id="bottom"></div>
</form>
If that won't get it or causes other problems, probably this can be addressed by setting the the top margin of the bottom tag and/or the bottom margin of the form tag to less than the default. This can vary from browser to browser but not as much as some other style variations so a happy medium that works for most or all browsers can usually be found, ex:
HTML Code:
<form style="margin-bottom:0;">
blah blah
</form>
<div style="margin-top:0;"></div>
Negative values may be used if needed however, if any value other than zero is used, units must be specified. Pixels should be fine, ex:
Code:
margin-bottom:-3px;
If you need to resort to negative values, this may render a portion of the content invisible in some (especially Opera) browsers. If this happens, setting the z-index of the partially visible element to one will resolve that:
HTML Code:
<div style="margin-bottom:-5px;z-index:1;">
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