Below is how you can detect non-ascii characters with javascript.
s = $("#something").val();
for (var i=0; n = 128) {
alert('Invalid character '' + String.fromCharCode(c) + ''');
return false; // or throw an error
}
}
Of course if you have to take in non-ascii values, then be prepared to set up your environments first. The links below will help.
http://us.php.net/manual/en/function.base64-encode.php
http://pureform.wordpress.com/2008/03/23/make-your-website-completely-utf-8-friendly/
BrianChan.us 