Loading random SWF into MC

So I’ve spent an entire day trying to make my old AS2 file that loaded random swf’s work with AS3 with no luck. Every time I think I’ve found the code to fix it, nothing works. The search here yields results for AS2, but not AS3. I’m ready to throw my laptop through the window at this point.

I’m new to AS3, so bear in mind that I’m a newb. I need the ability to load random banner ads into a movie clip in my main flash swf. Any help would be appreciated.