Downloading omnigraffle files from websites
 

We've been trying to post .graffle files on our websites at my school, but they do not download properly. (We use Macbooks; most of us are on Leopard, but some are still on Tiger; we use both Firefox and Safari)

Is it because they're package folders? Do I need to set the mime type on my website? Does anyone know what the proper mime type is for omnigraffle files?

Any help would be much appreciated - thanks!