I'm pretty sure it hasn't changed since CS3 (in fact It's been the same for as long as I can remember): in
Edit > Templates > Render Settings >. Another way of getting to this dialogue is from the
Render Settings drop-down in the render queue. At the bottom of the list of templates in the drop-down is
Choosing that brings up the dialogue box pictured below. Up the top of the dialogue box you'll find
Movie Default; set that to whatever template you want to be the default for renders. If you haven't got a template that has the settings you need then you can make one here - hit the
New button, set all your settings and give it a name. I find duplicating an existing one and modifying it a useful way to go.
Same goes for the output modules, which you get to from
Edit > Templates > Output Modules, or from the
Output Modules drop-down in the render queue.