Correct. New Macs have got FireWire 800, instead of the FireWire 400 that old Macs, like the ones with a Intel Core Duo processor had. In this case, you can get, for example, a FireWire 400 to FireWire 800 cable like this one > http://www.amazon.com/Oyen-Digital-Firewire-1394B-Cable/dp/B0027DPM1U
Actually, it depends on what model iMac the OP's i7 is.
The i7 iMac models had a FW 800 port prior to the current models released last fall.
However, late 2012 iMacs do not have native Firewire ports of any kind. They DO have one or more Thunderbolt ports, in which case the OP will need to get an Apple Thunderbolt-Firewire adapter in order to connect firewire devices.
I have a Firewire port ... and now have my camcorder hooked up via the 4-9 pin firewire cable I just bought ... but alas ... the camera is not showing up in the Device list in the Finder and Final Cut Express 3.5.1 says: "Unable to locate the following external device: Apple FireWire NTSC (720 x 480) : /
Though when I open System Information under Hardware > Firewire it is showing my camcorder is connected.
Any suggestions for how to get my camcorder seen by Finder and Final Cut Express 3.5.1?