test your alpha by clicking on the little white square at the bottom of your comp window (next to the red/green/blue little squares). Or set your background colour to something like hotpink so you can see what will be transparent.
Make sure when you render that you set your export settings to include an alpha channel, or RGB+A, or 32bit. Rendering as a TGA sequence is a pretty safe format that most NLE’s will be able to read the alpha. Otherwise quicktime animation codec or AVI uncompressed are good too.
Cheers
Michael Duff –
Southern Cross Ten, Australia