Code for a multi-select listbox / combobox

[Celinio Fernandes]

Hi,
I need to add a listbox / combobox which allows the user to choose several values.
I know there is one already available in the GWT API
http://google-web-toolkit.googlecode.com/svn/javadoc/2.2/index.html?overview-summary.html
with isMultipleSelect() set to true.
But the problem is that this version takes too much space.

I am looking for something like that (second one on that page, the picklist) :
http://www.smartclient.com/smartgwt/showcase/#multi_select_combobox_category

Can anyone share some code for that kind of list box ? I do not want to use Smart GWT at the moment.

Another cool idea would be to add a small button on the right of a textbox and when the user clicks on that small button,
a pop up opens and the user can select values from that popup by checking them (checkboxes) and that would automatically
populates the textbox (values separated by commas) when he closes the popup.

How do i implement such widget ?
I am looking for samples, ideas, suggestions ...

Thanks !