Here is a link Richard Snow posted earlier that really helped me
http://frontpage.dallas.net/~markp/collimation.html
It gives details on Collimation. It also talks of a spot that is put on the primary mirrors on some types of scopes that is to help with collimation. This may be the spot you see on your mirror. It would be located directly in the center. It also tells of a tool your can buy that makes collimation easier. I plan to buy one.
Anyway read the link, it gives step by step instructions on collimation, and should help. It may also explain the spot on your mirror.
