Scott Roberts has a tips and tricks post around the Office 2007 Contact Selector control that you can add to your InfoPath form: InfoPath Team Blog : Open your rolodex from InfoPath using the Contact Selector
It is not a built-in, first-class control, meaning that you'll have to do some work to get it integrated into your form 100%. But it's a lot easier doing all that vs. writing your own control from scratch.
email: Eric_Richards at ericri dot com
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