<script type="text/javascript">
function submitForm(action) {
var form = document.getElementById('form1');
form.action = action;
form.submit();
}
</script>
...
<form id="form1">
<!-- ... -->
<input type="button" onclick="submitForm('page1.php')" value="submit 1" />
<input type="button" onclick="submitForm('page2.php')" value="submit 2" />
</form>