Windows Multi-Monitor Systems
To provide Windows multi-monitor system users with a way to share specific information from just one monitor, GatherPlace recommends that you choose specific applications to share and move those applications to a single monitor.*
Using this method will make it easier for the presenter to manage the session while still having other non-shared applications on their other monitor(s) that are not necessary for the presentation.
See this article for information on Windows application sharing.
*
Available on Windows computers only. Mac application sharing will be available in the future.
Macintosh Multi-Monitor Systems
On Macintosh computers with multiple monitors
only the primary monitor is shared.
Therefore, you are able to place the desired applications/windows on the primary monitor and move the other windows/applications to the second or third monitor where they would not be part of the presentation.