FWIW, there is thread at the Microsoft Answers site regarding this font issue, as well as a new Outlook Tip created in response to the issue raised in that thread. Also here.

FWIW, as of this writing the font change desired (for RSS feeds) is not possible for Outlook 2007 because the necessary macro does not show in the "run a script" option in the Rules Wizard. But the problem is being worked on.