Submit form when return key is pressed?

On some browsers (IE) this form is cleared when return is pressed. I would like it to submit the form when return is pressed. It works on Safari, but I need it to work on IE too. Is there a way to do it? Here’s my form code (abridged):

<script type=”text/javascript” language=”javascript”>
<!–
function validate(zipinfo)
{
if (zipinfo.z.value == “”)
{
alert(“Please enter a 5-digit zip code.”);
zipinfo.z.focus();
return (false);
}
window.open(‘http://www.zipwise.com/info-tool.php?z=’+zipinfo.z.value+’&loc=’+location.href,”,’toolbar=0,location=0,directories=0,status=0,me nubar=0,scrollbars=0,resizable=yes,height=300,width=350′,true);
}
//–>
</script>

<form name=”zipinfo”>
<input name=”z” type=”text” id=”z”>
<input type=”submit” value=”Submit” onClick=”return validate(zipinfo);”>
</form>

Thanks for any suggestions.

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