A coworker of mine has been doing a lot of work  for a different client who is building several custom  MOSS publishing  sites, so I pinged him to see if he could duplicate my problem. He opened up one of his sandbox publishing sites, checked  the web  part gallery  and lo and behold, there's the rss  Viewer Web Part. He added  it to the page, pointed it at my RSS feed, and it rendered without a hiccup. Needless to say I was puzzled and frustrated.



So we started looking at the configuration of his site, and immediately I noticed that he had some features enabled that I didn't in my publishing site, specifically the ones relating to Enterprise licensed functionality. So I went back into my publishing site  and enabled the following two Features:

Office SharePoint server  Enterprise Site Collection features - this is enabled in the Site Collection Features link located in the Site Collection Administration section. Enabling this feature is what put the RSS viewer  web part  in my publishing site's web part gallery.
Office SharePoint Server Enterprise Site features - this is enabled in the Site features link located in the Site Administration section. You do not need to enable this feature to add  the web part to the top-level publishing site, but I think it is a good idea to enable both of these features in tandem.
Once I had the RSS Viewer web part in my gallery, it was smooth sailing. The feed  displayed, and I tweaked the XSLT in the web part to customize its output  to meet my design requirements.



I'm having a hard time  understanding why I need the Enterprise features to get the RSS Viewer web part, but that's the case. It just seems strange, since that web part is available in other standard  license site templates, that you can't get it in the publishing site template. The only thing  I can figure out is that it is assumed you'll be enabling the Enterprise features as a standard practice for publishing sites, which I guess I'll be doing in the future as a standard configuration step.