Testa detta:
<script type="text/javascript">
<!--
function checkLowerCase( o ){
var regexp = /^[^a-z]*[a-z]+[^a-z]*$/;
if( regexp.test( o.elements[ "n1" ].value ) || regexp.test( o.elements[ "n2" ].value ) || regexp.test( o.elements[ "n3" ].value ) ){
alert( "Fälten får ej innehålla gemener" );
return false;
}
};
//-->
</script>
...
<form onsubmit="return checkLowerCase(this)">
<input type="text" name="n1">
<input type="text" name="n2">
<input type="text" name="n3">
<input type="submit">
</form>
