There are a few ways to set up a private topic here. If you look at the bottom of someones post you should see a button that says "PM". If you hit that under a particular user then that will start a private message with that person. The other way that I know of is to go to the top of the page, you will see a few links (logout, search, links, your profile, message inbox, and help). Click on message inbox and then click on new topic. It will ask you which user you would like to start the topic with. The message inbox is also where you will go to read responses. When you get a response it will show the number of replies next to the message inbox link.