multi-select combobox (or an alternative?)

[caultonpos]

Does anyone know of a good (open source or free) multi-select combo
box? Or a multi-selection list that does not require 100x100 pixels to
be effective?

I have a common need for a control on a form or embedded in a table in
a spreadsheet type mode where the list of items may be 4-20 and the
user should be able to pick them as if checking checkboxes on a form.

This is for a nursing flowsheet so space conservation is important, as
is speed of data entry. Right now I have jtable working with type a
value, press enter and it goes to the next cell - just not sure there
is a perfect multi-item select control...

Greg