The bandwidth requirements vary based on the monitor resolution of your computer, the quality you choose to transmit at, and the nature of the application.
Generally speaking, any user with an internet connection should be able to participate in a GatherPlace meeting.

Some things to note regarding bandwidth:

• We recommend 1024x768 screen resolution and sharing at the High Quality [default] setting.
  
• Adjusting the quality setting to a lower setting sends less data while a higher setting will send more data.
  
• The system only sends presentation updates when a screen change occurs.
  
• Modem users are fully supported.
  
• We use an optimized adaptive bandwidth manager which automatically adjusts the amount data based on your connection to keep you in sync with the presentation.
  

For more information on how the quality levels compare, please see this article.