Edit in JSFiddle

    $('#show_all').click(function() {
        $('#display_none_select').find('option').show();
        $('#hide_options_select').hideSelectOptions(null);
    });

    $('#show_group1').click(function() {
        $('#display_none_select').find('option:not([value=])').hide().filter('.group1').show();
        $('#hide_options_select').hideSelectOptions(':not(.group1):not([value=])');
    });

    $('#show_group2').click(function() {
        $('#display_none_select').find('option:not([value=])').hide().filter('.group2').show();
        $('#hide_options_select').hideSelectOptions(':not(.group2):not([value=])');
    });

    $('#show_none').click(function() {
        $('#display_none_select').find('option:not([value=])').hide();
        $('#hide_options_select').hideSelectOptions(':not([value=])');
    });

<p>
    <input type="button" id="show_all" value="Show All" />
    <input type="button" id="show_group1" value="Show Group 1" />
    <input type="button" id="show_group2" value="Show Group 2" />
    <input type="button" id="show_none" value="Show None" />
</p>
<p>
    <h5>Using display:none (works only on IE and FF)</h5>
    <select id="display_none_select" multiple="multiple">
        <option value="">--prompt--</option>
        <option value="1" class="group1">option1 group1</option>
        <option value="2" class="group2">option2 group2</option>
        <option value="3" class="group2">option3 group2</option> 
        <option value="4" class="group1">option4 group1</option> 
        <option value="5" class="group2">option5 group2</option>
        <option value="6" class="group2">option6 group2</option> 
    </select>
</p>
<p>
    <h5>Using hideSelectOptions</h5>
    <select id="hide_options_select" multiple="multiple">
        <option value="">--prompt--</option>
        <option value="1" class="group1">option1 group1</option>
        <option value="2" class="group2">option2 group2</option>
        <option value="3" class="group2">option3 group2</option> 
        <option value="4" class="group1">option4 group1</option> 
        <option value="5" class="group2">option5 group2</option>
        <option value="6" class="group2">option6 group2</option> 
    </select>
</p>