Like the nav bar.
Search engines tend not to rank zero-content front pages very highly, so you will need to put a lot of work into promoting it.
Also, you can detect the presence of Flash using Javascript, so you don't need to always have the link on the front page. You can create a layer, name it, and then use Javascript to write the link info into that layer if the plug-in detect fails.
You do know that IFrames don't work in NS4, don't you?