Can'toper eps file

I received a .eps file (actually two of them) and cannot open it. I tried two different macs (Tiger & Leopard). Tried Illustrator CS 2, 3, 4, & 5. Tried Distiller and preview. Tried to import to InDesign, Illustrator & Quark. I keep getting "The file is in an unknown format and cannot be opened.
Emailed it to a friend who opened it immediately (Leopard & CS5), saved and returned a working file. What's up? Any thoughts? I can't keep emailing people to open my files for me.

Thanks