gif files to imovie hd

What do you mean by a flat file, I suspect you are taking a reference and not the file itself, but I can't be sure.

I see, animated gifs wont work that way, try dropping the download on your web browser.

Unfortunately you cannot use animated gifs in imovie, you may be able to separate the frames of the animated gif in preview or some other program, but you are going to find it very difficult to import them into imovie. Not saying it can't be done, just a lot of work, let us know if you are serious about doing this and I'm sure the regulars here will show you how.

To add a gif to imovie, first control click on the gif file in your web browser and save the file. You will then have to open it a program that can save it as a quicktime movie. I use Adobe ImageReady. After opening it in ImageReady you choose File>Export Original and select the Quicktime format. You can now import that file into your imovie as a video clip. You can probably do this with Quicktime Pro or Graphic Converter also. These would be less expensive optoins

You're going to have other issues once you've converted the animated GIf file. Dimensions.
iMovie wants to make 640X480 (720X480 as DV Stream) and a direct import of a tiny 100X100 GIF will be stretched to match the aspect ratio and dimensions of your iMovie Project. Ugly.
QuickTime Pro is the tool to use. It can import your GIF file and convert it to DV Stream. You can also add a background image so you can position your GIF track over it to allow the transparency color be used.