It sounds like you are looking for some moving background behind your text. There are a number of ways to do this (very cheaply). There are a number of places you can get animated backgrounds. Using pan/crop and/or track motion you can squeeze a full-frame animated background to fit the space you want to be filled behind your text.
Sony sells some such backgrounds - called the "Vision Series".
Also check out www.kickbacktracks.com where you can get some for about $30 I think (I don't have any personally)...
Then if you have a bit more money in the bank (like $500-$600) there is the Editors Toolkit from Digital Juice.