The recommended desktop video conferencing package for most users is Microsoft's NetMeeting. Although this does not address audio and video conferencing, it is a step in the right direction.
Application sharing is a very important component of remote collaboration.
Netopia's web site has a link which will download an evaluation copy of the newest Timbuktu. It has been tested here, and does work as advertised. The opportunity to try out the product is valuable. It requires MacOS 8.0 or higher. Timbuktu is a commercial product, so Macintosh users will have to buy a license for an individual copy if they wish to share applications with NetMeeting users after the evaluation copy expires.