Bill it's easier than you might think. The idea is to plane two tapered strips, checking every 4 or 6 inches for the correct thickness. Glue the strips together and plane the untapered sides until they measure up.
By setting your plane to remove less than a .001" shaving you can adjust things very slowly.
The hardest part is getting your plane blade really, really sharp. I built my first PMQ over a weekend. The only tools needed are a good hand plane, a dial caliper for measuring thickness and a box of 'binder clips' (giant paper clips from an office supply store) to use as inexpensive clamps.
The 'Planning Form' newsletter had a great step by step article a few years back, they are happy to sell back issues.
There are also several articles on PMQ's at the Bamboo Rodmakers Tips page...
[This message has been edited by kengore (edited 18 February 2006).]