Yes, but there's a big difference in what you need depending on the video mixer you get:
If you have an
analog video mixer (like an
Edirol V4) you will connect your cameras to the mixer via analog composite or S-video connections; plus you will need an analog-digital converter (like a
Canopus ADVC-110) between the video mixer and your Mac. You will have an analog connection from the mixer to the converter; and a Firewire connection from the converter to the Mac. In this case you will
also need to connect your mics (or audio out from the cameras) to the audio-in of the converter.
If you have a
digital video mixer (like the
Focus Enhancements MX4-DV) then you can connect your cams to the mixer via Firewire and also connect the mixer to your Mac via firewire.