I embed an external swf in flash builder like so:
[Embed(source="assets/sounds/mytestswf.swf")]
private static var mySwf: Class;
How can I access it and add it to another sprite on stage?
i don't think you need a loader, that's for libraries that are added at runtime. Embed compiles the assets directly in the swf, so addChild(new mySwf());
is enough to add it to the the display object list.
obviously, you'd like to assign it to a variable, so
var $mySwf:mySwf = new mySwf();
addChild($mySwf);
On a side note, you should name your classes consistently. Class names start with the first letter capitalized, so you can tell it apart from variables
[Embed(source="/assets/sounds/mytestswf.swf")]
private static var MySwf: Class;
...
var $mySwf:MySwf = new MySwf();
addChild($mySwf);