At least, according to [link|http://support.microsoft.com/default.aspx?scid=kb;en-us;890402|MS]

If that is not an option, check if NT4 drivers have snuck in. (They live in %winroot%\\system32\\spool\\drivers\\w32x86\\2). NT drivers can create havoc on servers where multiple desktops can be active (like Citrix and Terminal Services)