Yes.
Guests can be passed Presenter rights by the GatherPlace Host as long as they meet these requirements:

• The guest must have Java version 1.3 or later installed.
  
• Java is enabled in the guest's web browser.
  
• The guest accepted the Java security warning when the applet loaded.
  
• The guest is not using the SureView viewer to participate in the meeting.

Guests can test their browsers for compatibility at the GatherPlace test page located at: http://www.gatherplace.com/test
Windows or Macintosh guests can optionally download the free Guest version of the GatherPlace GP4 software to join a meeting which will also allow them to present in the meetings.

Please see this article for instructions on making a guest the presenter.

Note: The host and guest do not need to be on the same operating system for the guest to become a presenter.