Use the Web Developer toolbar in Firefox, and click Forms|Display Form Details to make sure the ID/name has been set correctly.
http://www.hanselman.com/blog/WatirMakerWrittenAgainInRuby.aspx
http://www.hanselman.com/blog/content/binary/WatirMaker.rb.txt
http://www.tonybunce.com/PermaLink,guid,ff4e1efc-ecd1-4078-b171-a3fe86807aea.aspx