<select> problem with wp-admin.css?ver=20081210

This is in version 2.7. Not sure if it is any other version as my website has been upgraded.

The problem I am having is I am building a new plugin. it uses a <select> tag to allow multiple options to be selected.

<SELECT NAME="categoryselect" multiple="multiple" SIZE=5>

    				<option value="0">None</option>
            <option value="1">Presistant Browser Based Games (PBBG)</option> <option value="2">Multi User Dungeon (MUD)</option>
  			 </select>

This seems to work just fine if I do not use this CSS sheet.
<link rel=’stylesheet’ href=’https://xxxxxxxxxxxxx.com/wp-admin/wp-admin.css?ver=20081210&#8242; type=’text/css’ media=’all’ />

Is there a class that is causing my problem? I need to be able to select multiples and this is causing me some issues as I cannot select anything.