Well, what I like to do is find the clip I want, take my camera and plug it into my TV, and start recording at the desired location. After that, I use iSquint to convert videos into MPEG-4 format (note: I only convert the videos in order to put them on my iPod or import them into iMovie).
If for some reason your camera lacks this ability, you can go to any Best Buy and get something called a "capture card". You can put the video on the capture card and then put it on the computer. the capture card works like a camera in that it acts as a "transportation device", if you will, for the particular clip you are moving to your computer.