Either force install Hpricot 0.6 (your usual stuff will still use the newer one, rfeedparser will use 0.6) or go mangle with rfeedparser to remove the lock to that version (of course, that removes any guarantee of it working 100%).

BTW, today is an awesome day to write a new feed parser. Here's why:

http://www.rubyinside.com/nokogiri-ruby-html-parser-and-xml-...