When do you run this on a page/form to split the name field before it posts to Infusionsoft?

name_split.js

<script type="text/javascript">
	jQuery(document).ready(function($) {
		jQuery('#Submit').click(function() {
			var splitName = jQuery('#Contact0FirstName').val();
			var names = splitName.split(' ');
			var firstName = names.splice(0,1);
			var lastName = names.join(' ');
			jQuery('#Contact0FirstName').val(firstName);
			jQuery('#Contact0LastName').val(lastName);
			jQuery('form').submit();
			return true;
		});
	});
</script>

did you try to alter line 3 to:

jQuery('#Submit').click(function(e) {

and add right below that:

e.preventDefault();

Hmm, thanks. I'll try.