Maybe you're running a whacked system, but I've been able to open every single FLA I've downloaded. Don't try to double-click the unzipped file. Instead, open the file from WITHIN Flash via the File--> Open... menu and select "All Files" from the "List Files of Type" drop-down menu. The 'strange format' file will appear, and should open right up for you!

I'm running a G3 with OS9. See if this works for you, and keep breathing!