I have an EyeTV Hybrid ready and waiting for my 27" iMac. I've tried it with my MacBook and it works flawlessly! The recording features are top notch and you can even buy the iPhone App to schedule recording or stream TV to watch on the move 
Call your cable company (or visit one of their service centers) and ask them if the firewire ports on your box are enabled. If not, ask them to give you one that has firewire enabled ports. They are mandated by law to provide you with one upon request.
Then try using a six-pin to nine-pin firewire cable (for the firewire 800 port on your Mac) or 6 pin to six pin cable (for a firewire 400 port on your Mac). I got it to work using the latter type cable with my Explorer 4250 and late 2006 24" imac.
Here's a decent tutorial:
http://www.blyon.com/blog/index.php/2009/07/01/watch-cable-tv-with-your-mac-via-firewire/
Good luck!![]()
-PN