It depends on where you put it, but it will be something like http://web.me.com/username/flashfolder/flashfile.swf
Basically in your iDisk you'll see a folder called "Web" and in there is "Sites" that the root level for http://web.me.com/username/HERE> Then whatever you named your flash folder in this location (perhaps "flash"), then you probably put your swf file in there. Hence the URL above.
Another tip to save battery life that the video didn't mention is to make sure that "Sound Check" is turned off. This feature makes it so all your songs are about the same volume, but it also using quite a bit of battery life.
Flash Video in iWeb