Here's the how-to on checking codes, it's a PDF file:
http://www.subaru-svx.net/photos/files/How-To/33055.pdf
If you can't open it, remove the drivers side kick panel (under the fuse box, just pull it off) and you'll see two big blue wires that have open ends. There will be a bunch of electrical connecters as well. You need to find a black connecter which has six slots along the bottom and 4 across the top row with a clip in the middle of the top row. Hold it with the clip upwards and the holes facing you. Plug one of the blue wires into the inner top left hole (the one beside the top left corner). Turn the ignition to on (don't start) and watch your CEL. Every long flash = 10, and every short flash = 1. It will run through all of the codes and then repeat until you remove the key.
Hope you can make sense of my rambling
