Problem 1: something related to prototype. There is something wrong that I could not proceed the checkout. Also, under cart, I'm seeing some error under form.js. Maybe there is something conflicting...
The dev store: [url removed, login to view]
Just add some item into the cart, inspect under firebug, and you will see the error: TypeError: [url removed, login to view] is undefined
Goto checkout and try to register a new customer. It is not possible to advance, if you'll go into firebug console: TypeError: element is null