<form action="" method="post">
<input name="qwert" type="text" size="5" maxlength="5">
</form>

<form action="qwerty.php" method="post">
<input name="qwert" type="text" size="5" maxlength="5">
</form>

<script TYPE="text/javascript">
<!--
function numbersonly(myfield, e, dec)
{
var key;
var keychar;

if (window.event)
key = window.event.keyCode;
else if (e)
key = e.which;
else
return true;
keychar = String.fromCharCode(key);

// control keys
if ((key==null) || (key==0) || (key==8) ||
(key==9) || (key==13) || (key==27) )
return true;

// numbers
else if ((("0123456789").indexOf(keychar) > -1))
return true;

// decimal point jump
else if (dec && (keychar == "."))
{
myfield.form.elements[dec].focus();
return false;
}
else
return false;
}

//-->
</SCRIPT>

<FORM METHOD=POST>
Number:
<INPUT NAME="dollar" SIZE=5 MAXLENGTH=5
onKeyPress="return numbersonly(this, event)">
<INPUT TYPE=SUBMIT VALUE="go">
</FORM>

<input type='text' name='qwert' value='' maxlength=10 onKeyPress ='if ((event.keyCode < 48) || (event.keyCode > 57)) event.returnValue = false;'>

<input type="text" name="qwert" maxlength="10" onkeypress="return testKey(event)">

<script type="text/javascript">
function testKey(e)
{
var key = (typeof e.charCode == 'undefined' ? e.keyCode : e.charCode);

if (e.ctrlKey || e.altKey || key < 32)
return true;

key = String.fromCharCode(key);
return /[\d]/.test(key);
}
</script>