The issue of the inability to open documents protected with AD RMS with Microsoft Office 2003 has now been resolved with a hotfix. You can obtain the hotfix at the following locations:
Office Client – KB978551
Word Viewer – KB978558
Excel Viewer – KB978557
Update (2/10/2010) - We recommend that AD RMS users download and install the update for AD RMS clients. This update ensures that any application with an expired manifest will be able to open protected content. If you have this update, the hotfix for Microsoft Office 2003 is not necessary.