I had a free copy of a steganos proxy randomiser on a coverdisc which can change proxy every 5 seconds if you want it to. The problem with it was (apart from slowing the machine down majorly) that the automatically updating list of proxies it uses contains proxies on port 80, which are useless on ntl, and if you remove them from the list manually it rebuilds itself.
You might try taking a look at the free
Jap software as well.