How would you go about connecting tally port that to your Mac?
Those guys also have ethernet and USB ports. Can you control the tally lights from those?
I would guess that you can drive the tally lights by pulling the specific pin down. If you're feeling brave, you could test that theory by connecting pin 1or2or3 to pin 4 on that DB9. If that's right, you could probably drive the lights with some of these. http://www.phidgets.com/products.php?category=9&product_id=1014_2
I think the "Applescript Effect" idea would be the most flexible. Let me know if you can get those things connected to your Mac and you have some way to control the lights.