Expandable ad

I am trying to create an expandable skyscraper ad in Flash. I have downloaded the Motif Ad Kit and files, but I still do not understand how this is done. Their ads are for banners, and I need to create skyscrapers. Does anyone have any tips that would help me understand the concept behind this?
I thought I’d have to create two swfs, and link them together somehow, but it looks like they are creating these expandable ads in one file, with the size set to the expandable size (320x600). When I try to upload these to my server, it crunches the entire ad into the ad space alloted on the site (160x600), so it looks like it’s at 20% horizontally, but 100% vertically. I am not using an ad server for the ads - they are just stored on my website, so I don’t know if that has anything to do with it.

Thanks for anyones help!