Capturing analog video in FCP 7

I teach a high school TV Broadcast class and we still have ten Canon ZR900 mini-DV cameras that take great video (we also have some SDHC video cameras). BUT....the firewire ports on the ZR900s no longer work and we are unable to upload video from them. Is there any practical and efficient way to use the analog RCA cable (which we mainly use for monitor playback) to capture video in Final Cut Pro 7? I hate to see these otherwise excellent student cameras go to waste. I have purchased a Diamond brand analog video capture device as well as something similar called EasyCap. They both have the RCA input lines for audio and video as well as S-video inputs (on one end) and a USB input for the computer. I just can't figure out a way for the iMac to recognize these devices. My next step is to plug the thing in to my old ilo DVD recorder and see if that will accept it. But that capture method is not very practical for a high school class. Any suggestions? Thanks.