iChat will work with any Firewire camera, or any USB video device class webcam. Keep in mind the USB one is a recent standard, and many older webcams do not support it, instead relying on proprietary drivers that rarely are coded to work on OS X. The XBox 360 camera works with iChat, though you will also need a microphone too. No Mac comes with a mic input onboard, only a line level input.

A MacBook (non pro) is going to be about the same as the Mini. They do offer slightly faster processors, and a slightly faster integrated graphics solution, but the difference will be minimal. The Mac Minis are long overdue now for an update, while the MacBooks were recently upgraded (see the buyers guide here.)