Help! How do I open a winmail.dat attachment with my Mac OS 10.6.8 & Mail 4.6 (1085) Thank you.

See the Mac OS X Mail: What is a winmail.dat attachment? (HT2614) document; either obtain a tool to unpack the winmail document, or ask the Windows user to update your entry in their address book to not use the winmail stuff as described in that HT article. There are some more articles on this topic off to the right in the More Like This section, too.