In the sx's they're below the vents right?
If so you need to get the vent fascia off, should just be a couple of screws beside the steering column, then it will pull off with a bit of fiddling to get it around the steering rack.
From there it should be self explanatory.
If it's up the top, as in the same height as the instrument cluster then you need to take the above piece off, and take off the instrument fascia, it has screws from underneath going up into the dash, then it comes out.
Wiring - Use a multimeter just to get your +12v, and acc. Ideally it's a good idea to run a new +12v with some 30amp rated cable either direct from the battery or tap into the +12v on the ignition barrell. If you want to use the original speaker wire (personally I'd just run new stuff) then work them out by trial and error by twisting pairs and see which speaker emits sound. They're colour coded to a degree, you should be able to figure it out.