I'm trying to use the modals within Twitter Bootstrap to implement a contact form.

Ideally I would like the first two fieldsets to align next to each other and the third fieldset (containing a textarea and a submit button) to occupy the full width of the modal.

I have tried to use rows and spans to make them play nicely but am not sure on the way to go about this. It seems like there isn't a total of span12 to start with.

Has anyone else achieved anything similar?