I am not 100% sure what is causing this to load twice. I would like you to try a couple things though.
1. Something on your page loads jquery 1.6.4 from google api. If you could disable that temporarily, to see if that fixes it, that would be great.
2. If that doesn’t work, go into the PLugins Manager for the plugin and set the plugin to not load jQuery, and also to not use noConflict.
If neither of those two things work, would it be possible for me to get a temporary admin login to the Joomla backend? Is the site live?
Basically, from what I can tell, you have (at least) two versions of jQuery being loaded (1.6.1 and 1.6.4). I don’t know if this is causing the problem. It really shouldn’t be , but it could be the case.