Pressure points are not part of the basic curriculum most commonly found in Aikido.
Some folks do study them though, and post in these forums (much to some other folks' amusement).
I suggest you stick around for a while, they'll show up, and may give you more details.
I understand there's a Dr. John Riggs, who posts sometimes here that has written an article for black belt magazine on the subject(to be published)
Any discussion on the subject will be peppered with the good the bad and the ugly since it's a topic that inspires some level of heat..