Here’s a JavaScript auto-tab implementation that doesn’t have that most annoying of bugs: when you click or tab into a field that is already populated, it tabs to the next field, disallowing you from deleting or changing. This one only auto-tabs on keyup.
UPDATE: dag nabbit, I was wrong. Shift-tabbing back to the previous field doesn’t work right in Firefox. On the “var filter” line, add a 16 into the [0,8,9] list, making it [0,8,9,16], and you should be set.
Posted by Josh Justice 
