If I can take a crack at it. As jb says, you may have a problem if you already layed the pavers and are installing the timbers after-the-fact. You see, the ground under the pavers will continue to settle 'out' towards the timbers. So, you might want to do a real good job of packing the soil right where the pavers meet the timbers. Do it with a mallot and a piece of 2x4 or something if you have to. ANd pack about 2" at a time. If you try to pack too much at once, then you'll create air pockets.
Now, as for how to lay the timbers, buy yourself the timbers that are rated for BELOW-GROUND USE. I believe they're rated as a 3 on the timber. (Check w/the Building Supply Desk a the store.) Then, as a rule of thumb, lay the timbers out and on top of each other so that the 'end seams' don't over-lap a row below. As for the 90 degree corners (assuming it's square), the easiest way to describe what to do is to interlock the fingers of one hand with the fingers of the other hand, and turn them 90 degrees. See what I mean? SOoooo, when you go to cut the logs, you have to compensate for this measurement. Be sure to buy a few extra timbers for waste and possible errors. Draw the picture out on a piece of paper.
After you're finished cutting, start stacking. Use Nail Spikes to attach the timbers to each other at 3' intervals. (Nail the ends of the 2nd row of timbers to the first row and space them evenly inbetween, at a max. distance of 3' from each other. Closer if fine.) As for the 90 degree ends, I attach those last. WHen I'm all done, I use 1/2" drill bit that's 18" long, and pre-drill all the way through the timbers. I bore it out pretty good so the bit runs freely through my hole when I'm finished. Then, I get the most straight steel, concrete-reinforced rebarb I can find and drive it all the way through and into the ground! If your wall is more than 18" high, then at that point, do this step. The rebarb comes in 12" and 24" length for this job. In addition, I use this procedure every 8' or so along the 'run' of the wall to keep it from moving. The more rebarb in the ground, the more stable your wall will be.
Be sure to go through all this in your head FIRST before you start cutting and drilling and pounding. Try to anticipate any problems with the building of the wall. Again, draw your measurements on a paper and account for the 'width' of the timbers when you come to corners and when you figure the 'run' of the wall. Interlock the ends and DON'T overlay one row's ends where the row above or below will have its 'ends'.