The difference in the two platforms is not a factor in this current problem. Let's cover the basics first and then see how we get on. I am going to assume that you have a Broadband internet connection, Cable or DSL.
Make sure that your iSight camera is connected to the Firewire port of your Mac and turned on. Launch iChat, if it did not automatically launch, and go to the Preferences menu. Under iChat on the menu bar at the top of the screen. Select the Video Tab and make sure that the camera is recognized by iChat. Set the sound input to whatever you are using. Usually External Microphone/Line in. Make sure you actually have a microphone plugged in. You did not mention what computer you had and that can make a difference. iMacs have a built-in Microphone, Most of the Beige Macs do not. Put a check mark in the Automatically open iChat when camera is turned on. Put a check mark in the box below it too. Close the prefs window. Go to the audio menu at the top of the screen. Check to see that Microphone Enabled and Camera Enabled have a check mark next to them. if they don't put one there by sliding down to the first one and releasing the mouse. Repeat with the second one.
If everything is working correctly, you should be able to iChat/Video to your hearts content.
Let us know how you get on,
Hope this helps
I've been trying to video chat from my iBook to a friend's PC, (iChat to AIM) and it won't let me do it! I'm in OS X panther and he's in Windows XP and has a web cam, but the audio and video options are still greyed out. Can anyone help!?