most bike shops sell a motion pro shock spanner wrench for $15-25.... i use a generic spanner wrench set i got at harbor freight... but they aren't as good as the thinner motion pro ones.

 

Dcopp, a spanner wrench is the correct tool to use to set the preload on the front, but you can get away with using a small pipe wrench also. Just be careful not to damage the body, but it will work. On the rear a spanner wrench is the way to do it too, but if necessary, you can use a punch and hammer to break the lock rings loose. This can damage the lock nuts though if you are not careful.