Hi
You need to have your list of values into your secondary DOM in a repeating Table or section in a scrolling Region control and have another field which would be your boolean value for the check box By checking off check boxes next to items you could select multiple items.This will involve some coding.
If you are interested another idea is we have a tool called "Smart Combobox" which is actually a list box with multiselect option. An evaluation is present in the "Downloads" section of this site. You can test it out by downloading it for free.
And Another option is Office 2007 will provide this functionality that should also solve your problem.
Madhuri
http://www.ggktech.com