This is probably the wrong place to ask about adding repositories, but I remember when I was trying to work out what a repository was and how to add it that a few folk were less than helpful... so, your settings should read as follows:

Catalogue name: Extras-devel
Web address: http://repository.maemo.org/extras-devel/
Distribution: fremantle
Components: free non-free
Disabled: not ticked!

Save and enjoy.

I'd highly recommend not using this repo however if you don't know what you're doing... things are in development and could brick your phone etc etc etc.