Ian,
using the Tak collimation scope you should adjust the secondary first, such that the dot on the secondary is centered in the donut, then adjust the primary so that the bright ring around the edge of the mirror is concentric. Clear as mud? Then look at this link:
http://www.dosborne-astroimages.co.u...on_article.htm
or this:
http://www.rcopticalsystems.com/supp...ollimation.pdf
It doesn't matter that they are RC's, but they are using Tak collimation scopes.
Hope this helps,
Gary