It's a little unclear to me what you are asking. Do you provide content that you want to appear on a web page, and in a RSS feed? Or do you want to be able to syndicate content from an existing feed an incorporate it into your site?
We do a little of both on oldhouses.com. This page:
http://www.oldhouses.com/listings.xml
is an RSS feed that can be read by any reader. It is pure XML, but it links to an XSL style sheet that causes it to display as a page in a browser.
This page:
http://www.oldhouses.com/old-house-r...on-stories.htm
syndicates content from an existing RSS feed using Javascript and presents it on the page. We found an external script somewhere but you could roll your own using AJAX techniques.
Server-side apps like Cold Fusion can also grab RSS feed data and render it into an ordinary web page, so that's another option for generating searchable syndicated content.
We have just started working with RSS so I can't really tell you it affects rankings. The second page doesn't actually include the syndicated content, so I doubt that it impacts the rankings for the page.
Since XML tends to have a good ratio of content to code, my guess is that search engines will be able to spider and rank them effectively and in some cases are already doing so.
Joe