Sorry man, but most of my comments are critisism:
Disabling the backspace key is not something I would condone. Manipulating keyboard returns as part of form validation is, imo, a highly dubious practise which creates confusion for users. And doing it in order to "control" history navigation is even worse - you simply shouldn't be trying to do that, and it only affects unaware IE-users anyway, compounding the perception of that browser as a security monster with no respect for user's preferences.
btw - does cancelBubble really have that effect in IE? That doesn't make any sense, because keyboard events don't bubble.
I also disagree with the use of modal dialogues, whether on the web or in local applications. I consider them the last resort of bad interface design, forcing the user into a fixed order of input purely for the convenience of the author.
"Why bother with accessibility? ... Because deep down you know that the web is attractive to people who aren't exactly like you." - Joe Clark