FlexBuilder: automatically call program on build

[creynders]

I want to call SWFencrypter on manual builds and let it encrypt all the swf files built by Flex. I've tried project>properties>builders>new
and manage to let it call swfEncrypter automatically, but I can't figure out how to pass the swf files as a parameter to swfEncrypter.
Does anybody know a good tutorial for this ? (or better yet; can someone explain how to achieve this?)

[hangalot]

build with ANT

[creynders]

Thanks, but I'd rather do it in flex builder first.
But, if I can't figure it out, do you know of a good tutorial of how to do stuff like that in ant?