I recommend you get a repair manual if your going to work on your own vehicle. It's real easy now that they're available online. To be better prepared when working on your vehicle, read up on the job you're about to perform, it will show you component locations, bolt torque settings and what special tools you'll need. There are also technician tips related to your specific vehicle.
Try http://bit.ly/mitchell_repair_manuals_online and you can have one in minutes, for less than $30.00.
I am a 27 yr subaru tech and a core replacement is very lengthy and complicated because you have to remove the dash to do this. I suggest you do not attempt this with out professional guidance. You may end up with more than you bargained for.