Problems with winmail.dat attachments

Hi--I work in a large department full of Mac users using various Intel Macs and Snow Leopard, with Mail.app as our email client. There are a couple of Windows users using Windows 7 and Outlook as their mail program. The Outlook users have had their preferences set so they are sending HTML mail rather than RFT-formatted mail. When they send attachments, some of us get readable attachments (they're usually Word and PDF files) while others get unreadable winmail.dat attachments. None of us have downloaded any of the various file conversions programs available that do this conversion automatically. This suggests to me that there is some difference in some setting somewhere on the Mac that enables some of us to read these attachments while others of us cannot. I can't find it anywhere, though. Does anyone know what this might be? It does not seem to have anything to do with what exact version of Snow Leopard we are using--there is some variability, but the variability occurs both among the people who can view the attachments and those that can't.

Many thanks,

Marc