Mac Fonts...why are some "UNIX EXEC" and wont work as a font?

The suggestions to zip the files that the client is sending you is a good one. The other is to ensure that there is an extension associated with the font (or with any file).

You may have heard about "resource forks" and the confusion that can arise when sending files between computers. The end result is often a little "Unix Exec" file that won't do anything intelligent when you double click it. The problem is that the computer doesn't know what kind of file it is -- the easiest way to make sure that the recipient's computer knows what to do with the file is to name the file with an extension. E.g. for fonts, .dfont or .ttf. Not all fonts have extensions, but a lot of them do.

You may have to walk your client through zipping a file or turning on the Finder's "Show All Extensions" preference.

If you are sharing files through or coming from a PC network...

The PC (like LaCie Ethernet disks) knows, for your Mac's, only the "Apple Talk" protocol.

So on your Mac, just Activate "Apple Talk" in System Preferences.

And no more "EXEC" icons to see!