1: Add the comp to the render queue
2: Click on the link to the right of the output module (Lossless by default).
3: In the Output Module Settings dialogue, click on the topmost dropdown menu (format) and choose png sequence.
4: Change the Channels drop down menu from RGB to RGB + Alpha. In case you don’t know, the alpha channel is where the transparency info is kept.
5: Render and you’re done.
I see you want to export a targa sequence. I don’t know if this works as I normally just use png, so feel free to try this with targa.
Simon Bonner
youtube.com/simonsaysFX