Outlook 2001 can't send Word docs to PC's

[T]

When I send a Word attachment (with a .doc extension), it shows up at the
other end (for PC users only) as a .dat or .tmp file, full of gibberish.
Even changing the extension to .doc doesn't work. I've also tried sending
it as a .txt. Does anyone know how I can fix this?

Thanks,

T