codice:
<form name="form_1">
...
<input type="button" name="btn_submit" value="submit" onclick="javascript:dosomething();" />
</form>
codice:
<script language="JavaScript">
function dosomething() {
 if (document.forms[0].nome_elemento_tuo.value=='pagina1') {
  location.href='pagina1.htm';
 }
 else if (document.forms[0].nome_elemento_tuo.value=='pagina2') {
  location.href='pagina2.htm';
 }
 else {
  location.href='pagina3.htm';
 }
}
</script>
per esempio..