This actually speeds up the render slightly because AE doesn't physically have to refresh the screen for every frame it finishes rendering a frame. Start up your FCP project and open the sequence that your render is to be inserted into. Drag the freshly rendered file into the Browser. Now overwrite edit it into the sequence at your in point and play it back. Remember that if you get a red render line here, it means that either you chose Animation or some other codec to render with, or you got your settings incorrect somewhere.
Settings are everything.
The choice of a codec is an important one. Until very recently, it was generally agreed that the Apple DV codec gave sub-standard rendering results. DV compression artifacting was incredibly destructive to high contrast images, particularly text. Two developments have recently caused us to take a second look at the Apple DV codec. For those who shy away from beta versions, the 9.1 updater for Mac OS 9 offers another way out.