The way the d.net id at teamanandtech.com works is as follows.
When you add your d.net id to your teamanandtech.com profile, you are not joining Team AnandTech in the d.net projects. You are only providing teamanandtech.com with the ability to link from your profile to your distributed.net stats. The d.net id will be used in the future for providing db driven stats.
Every day at 10:00am UTC, teamanandtech.com gets a list of current Team AnandTech members from distributed.net, and adds any new users id's into a table. When you try to add your d.net id to teamanandtech.com, it compares the number you enter to this table. Thus if you are not a member of Team AnandTech at distributed.net, you will be unable to add your d.net id to your teamanandtech.com profile.
HTH!
Mika