If webcam chat or capture is important to you, spend your money on a new Mac first.No manufacturer I'm aware of provides an OSX app to support buttons atop a webcam.Some USB video devices simply will present an on-screen dialog: "This Device Requires A USB 2.0 Port".Frankly, Macs lacking USB 2.0 ports have hit obsolescence anyways.
Newer versions of Photo Boooth do allow selecting your camera input choice from the CAMERA menu.
Several companies such as Rocket Fish, HP, and Microsoft have 1 or more buttons on the camera to save an image snap to disk, send to email, or possibily to a printer.
However, only Windows software has ever been written to support them. i Movie is only designed to work with a i Sight on an i Mac or Mac Book - or a Fire Wire DV camera source.
They may or may not actively use chat programs, but at least this is a starting point.
Many social networking and adult profile sites often have webcam chat rooms you can join if you so choose. It's the most fully featured Mac/PC Cross-Platform webchat experience available. It has both G-rated and X-rated rooms to visit, online member status and more. It offers a built-in community you can browse & optionally connect with.