I'm still new to web design/development. I'm working on a data entry form for an internal system at work. On the form, the user can select an office from a list queried from a database. (The backend for this is PHP and MySQL, if you're curious.)
I would like to add the functionality to allow the user to add an office to the list, among other things, with minimal invasiveness. I don't want to use a popup window since the default behavior for company browsers is to block popups. I've seen this, which shows you how to create an alert alternative in place of a new window. To me that seems like basically the same thing, and not really an improvement except that it would keep the browser from putting a kibosh on the new form.
I think it might also be good just to keep the popup/alert functionality out of the picture altogether and opt for a new undisplayed <div> that is triggered by a button or doubleclick, autc. and closed by okay or cancel.
Like I said, I'm still new to web design/development, and I'm wondering what the currently accepted best practice is for accomplishing this task with the best possible user experience.
Update: the real question is "Is there a current best practice for accomplishing this task with the best possible user experience?" The answer may be "no, there are many options and none are more prevalent." What I'm looking for is either that, or "yes, the currently accepted best practice for user-experience in this case is X."

<div>but it still has the ultimate effect of popping up with a window of some sort (an alert in this case) rather than some other design that might be better. I'm trying to ask what design choice would be better than a popup. – user25791 Oct 6 '11 at 15:00