See http://www.w3.org/International/O-charset.en.php
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" > for HTML
<meta http-equiv="content-type" content="text/html;charset=utf-8" /> for XHTML (I've changed capitals to lower case as well as the closing tag / ).
Validators (and I think browsers) use utf-8 as a default if none other is specified.
To see what you have at present look for the meta tag in the head section to see what charset is there now.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.