How To Pass A Value In Visual Basic

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This is kinda tricky... and there may be another way to go about it. Basically I have a list box (contacts) which is populated by an SQL command, from my data environment. What I want is to pass only a single value at a time from the (contacts) list box to the attendies list box. So basically I can select from the list box contacts as people walk into a meeting and add them to the Attendies list box, one at a time. How the hell do I do this????