Dealing with winmail.dat and unreadable email attachments

This is a rare Outlook problem, but a good thing to know when you do have to deal with it:

Dealing with winmail.dat and unreadable email attachments: "Email users sometimes find that they receive email messages with a strange file attached, called winmail.dat. When they attempt to open this file, either it can't be opened at all, or it contains 'garbage' data. "