I've seen clips of film where a car, for example, is bright red...and the other colors in the picture are washed out, toned down, or desaturated, whatever you call it.

I'm working in Premiere Pro

Any guidance from the experts would be much appreciated.

One option is the "leave color" effect. Using your example, if there are other red items in the frame with the red car, you will probably need to mask off those areas away from the car.

So, on video 1, you'll have the unmask video, completely desautrated. On video 2, you'll have the same clip with the car masked off with the mask transparent to the layer below. Use "leave color" on the car color and tweak the colors so that only the car is red. You might need to adjust the mask if other things pick up the red.

All of this is in CS3.