Good Lord! I've just managed to open a winmail.dat file for the first time ever.
I downloaded this freeware application, which unzipped the attachment and revealed the 8page .pdf within.
Yes, I did know the sender and yes, I did trust him not to send me and all other recipients a virus/bug. He's the CEO of a large grain trading company.
Might help others with .dat attachments which you trust?
http://www.twistermc.com/583/open-winmaildat-files-mac/http://www.joshjacob.com/mac-development/tnef.php(If I've put this post in the wrong place, apologies, no doubt it will be moved to the right place as necessary.)
Now I just wish I had an "in" to .wmv files which my brother attaches now and them.