After some thinking, I guess you wanted to disable "Auto Complete" functionality in the browser. Right? The user can do this by visiting
Tools|Internet Options|Content|Auto Complete. ----I am talking about IE.
If you "brutely" disable the "auto complete", you overdo. I guess it would be a better idea to using an "alert" ask the user to disable "auto complete".
Sorry for having misunderstood your earlier postings.