Ok here it is.  The must anticipated timing belt change how-to.  Please note, that the first steps of this procedure is located in my "Unorthodox Racing Pulley Installation" how-to.  Please also note that I did not change my belt when I took the pictures.  So there are a few that would probably have been helpful that did not get taken.  However I will do my best to describe in VERY good detail these parts of the procedure.

ALSO NOTE!  If you are changing your timing belt, it very well may be time to replace your water pump as well.  For the time and aggravation that it will cause you not to, I suggest doing it at the same time.  Otherwise you will have to do this entire installation later when your car starts overheating!  My pump was brand new with seals, and thermostat for a whopping $64, right from my Subaru dealer.  :)

Getting Ready

First gather all the needed tools.  These are:

1. Basic socket set, wrenches and extensions (mostly just a 10mm, and a 12mm)
2. Torque wrench with a minimum strength of 115 ft/lbs!
3. Very small pin (damn strong one!) or a finishing nail (which I used)
4. C-Clamp or Vise (I used C-Clamp)
5. Pliers, or vice grips
6. Cover Seals (2 of them)
7. Timing Belt (obviously)
8. Patience!  :)

Continuing on from the other howto's removal instructions we will start with the removal of of the necessary brackets and pulleys.

A/C Pulley / Bracket

This piece contains 3 bolts.  All of which are 12mm.  Remove these and take off the piece (very simple).

Power Steering and Alternator Pulley / Bracket

This piece contains a total of 7 bolts.  All of which are 12mm, you will need various extension to remove these.  I start with the bolt holding the bracket for the alternator.  This allows me to move the bracket upwards to get it out of the way (see picture top left).  There is a bolt hiding under the ps pulley (see picture top right).  These are the mostly troublesome, there are 3 bolts behind the ps pulley.  Use a short socket too loosen and your fingers to work them out (see picture bottom left).  Finally remove the last bolts, on on bottom near pulley and one on the top of engine (not shown) you will see it (see picture bottom right).
 

Now simply lift up (GENTLY!) on the ps pump to maneuver the bracket out.  This final result is below (note you can not see the top engine bolt in this picture either).

Timing Belt Cover's (3 in total)

To remove these pieces you will have to remove the fans for the radiator.  There may be a way to work them out...but believe me its worth the 5 minutes it will take you to remove the fans, simply in extra work room.  Simply remove the 4 bolts to the radiator (10mm), and disconnect the electrical.  The fans will just lift out.

The covers come of relatively easily with a 10mm socket.  Simply work your way completely around all of the covers until all the bolts are removed (I didn't count them sorry).  Below is a picture of my center belt cover after my crank pulley came apart.  :(   Oh well, got me writing this I guess.
 

Belt replacement (the fun part!)

Ok now for the difficult part.  It really isn't that hard, just difficult to line up and get to stay correctly.  I am sure there is some wonder Subaru tool to do this, I do not own one, and I'm sure you don't either.  However some patience is all you need to get the job done.  Below is what your engine should look like without belt covers.

Believe me, when I changed mine it looked nothing like this.  It looked more like gears/pulleys covered in strings and peat moss!  My belt was totally shot.  This is my new one I installed two months ago.

Ok now on to the replacement.  The tensioner as seen in the below pictures is the main key to the process.  It is the easiest part to remove to get things lined up.  The other main part is the piston behind it (both seen in picture bottom left).

NOTE This is the portion where you would change your water pump!  It is located right at the bottom right hand side of the above picture (where the main coolant hose is).  I can't remember how many bolts it is, however it is fairly straight forward to install.  Now back to the belt!

First step is to remove the tensioner.  This will allow the easiest access to removing your old belt, and is the key to keeping the belt from slipping later when you are all done.  Simply remove the bolt and pull the pulley off.

Now for the piston.  The most important part of keeping tension on the belt is with this piston.  You will notice when you go to put your new belt on, that is appears to be WAY to big.  This is because the piston has not yet pushed the tensioner into place.  Remove the bolts holding the piston and take it out.  Now if you inspect your piece you will notice there is a small set holes drilled into it (best seen in picture bottom right).  The small hole in the collar of the piston is the key.  It will correspond with a hole on the shaft of the piston.  Take your C-Clamp or vise and compress the piston.  Do this carefully, as I would assume that this part is quite expensive.  Another thing to note is that you have the shaft hole and collar hole lined up (VERY IMPORTANT!).  Once this is done insert your pin (or nail) into the now lined up holes.  This will keep the piston compressed.  Be VERY sure that you leave a small amount of your pin facing out.  This will allow you to take your pliers / vice grips to remove it later (hence expanding the piston).
 

Now to put on your new belt.  Once again this is much easier with two people.  This will allow you to maneuver the belt while they hold it in place for you.  However I am sure this can be done with only one person as well.

First off you must locate all of the timing marks.  These are small arrows or marks on the vehicle that show when the engine is in time.  These must be lined up perfectly or you vehicle will not run!  (or at least VERY badly)  Below are pictures showing these marks.  Simply take a socket and turn the respective gear until the marks line up.  For the crank gear.  Re-insert your crank pulley bolt, and turn like the left/right side sprockets.
 

Now it is time to put on the new belt.  Line up the belt markings with the respective timing marks on the sprockets.  There will be one main belt marking, this is for the center crank sprocket.  This seems to the easiest place to start.  Have someone hold your belt in place once you have the marks lined up.  This is very tricky by yourself.

Once these are installed re-install the tensioner and piston.  Be VERY careful with the piston as its EXTREMELY strong.  I wouldn't want to be responsible for someone losing an eye from a broken pin!  Once these are bolted in (tensioner should be torqued to 29 ft/lbs!), you will notice that it not rests up against the VERY loose timing belt.  Hold it tight in place against the belt, so that your marks wont slip, and get ready with the vice grips.  Double check all marks are PERFECTLY lined up and take the vice grip and remove the pin from the piston.  The piston should snap into place holding the tensioner tight.

At this point pat yourself on the back.  The worst is now over.  :)

Finishing Up

Simple do the reverse of the above!  Your crank pulley needs to torqued to 115 ft/lbs!  Any less and your pulley is likely to come off or at least come loose.  NOT GOOD!  :)

Voila!  It's miller time!