three-column trouble

OK, I have a problem with my blog. I have three columns on my main page, but anything someone goes to a permalink, my third column gets banished to the outer darkness. What gives? Can anyone point me towards the healing and restoration of the third column on the permalink page of each post?

Oh, and while you're at it, I would love to have categories [for posts] on here but I'm not sure how to do that either. I am in need of some good, old-fashioned, modern enlightenment...