e-mail attachments in TNEF format

Our LAN consists mainly of Windows clients that use Outlook 2003 for their email. Somehow, when they send attachments to a MacOSX user, they are tnef-encoded thus making it difficult for the Mac user to open them (would like to avoid using an external tnef decoder because the mac user is a bit lazy and wants to just click on the attached file and open it).

Please note that outlook clients are NOT sending their emails in RTF/TNEF format, just plain text or HTML at most. In fact, the Mac user can correctly display their message body - only the attachments appear as application/ms-tnef.

Also, if a Windows user sends an email with attachement via Mozilla Thunderbird, webmail such as yahoo, etc., then the Mac user receives the data correctly and can open the attached docs with the click of a mouse. So it appears that it's an outlook-specific problem with tnef attachments (not just email body).

The Mac user has tried MS Entourage (which for some odd reason does not correctly decode Outlook's TNEF format, although it's the same company who owns both softwares) and Mozilla Thunderbird for Mac without any luck.

If we use the Mac OS 9 emulator and run Outlook for Mac then email attachments work fine. But of course we don't want to go back to OS 9 and Outlook is not available for OS X.

Has anyone experienced this before?

Any suggestions?

[EDIT]
I sort of solved this issue. Mainly, there are three solutions:
1) upgrade to Exchange 2003 (or even better: an open-source mail server)
2) avoid using Windows outlook clients
3) use Exchange 5/5.5 and Windows Outlook clients but configure Mac OS X mail client with a POP account, NOT IMAP. By using POP, Exchange does the TNEF conversion for you. The drawback is that Mac OS users cannot take advantage of the remote IMAP service.