I am trying to show a \'Post to Your Wall\' feed dialog with the following code in a facebook iframe app:
I'm pretty sure that you get a popup if the user has not authorized your application. Facebook made it work that way for security reasons. If you prompt for authorization first, then you should get the inline dialog.
Note that the request for authorization will itself be a popup, but you only have to have that happen once. I have things working this way, the way you want, in the someecards Facebook app. Feel free to grab the javascript code, it's not specific to the app.