Search.
The info is all on here. This forum format tends to not show older threads. Use the search function and you'll find tons more.
There isn't much in the way of power improvements that don't cost a fortune. You can bling it out with exhaust, a cold air intake (generally useless), lower it, better wheels/tires/brakes. Pretty much anything you can do to an Impreza you can do to a Foz.