I am using the latest version of After Effects to produce a Flash file video of me giving a company introduction.

This is the process I have used so far:

.Imported footage into After Effects as a high quality .mov file
.Keyed the file in after effects to remove my green screen
.Dropped the composition into the Render Que and set is to output as a FLV small for the web (the video is 90 seconds but needs to be under 7mb). I have also set it to crop at this stage.

However, I get a very dramatic loss in quality which isn't good enough for it's use.

My question: I need to use After Effects as it's the best programme for me to Key my very bad green screen in. How can I make a smallish FLV file (under 7mb) and still retain good quality?

I might need quite specific instructions as I am a newbie to all of this!
Thanks.