Just in case you missed it, Carol Bailey has posted yet another fantastic article on certificates over on the http://blogs.technet.com/configmgrteam blog. If certificates are as confusing to you as they are to me then you'll definitely want to give this one a good read. I have her intro and a link below:
I'm going to share some information about an option on the Certificate Services advanced Web enrollment page, because I couldn't find it documented anywhere and it took me a long time to work it out. However, even though I'm explaining how to use this option, I strongly recommend you never do unless your PKI admins insist. Why? Because it explains how to request a certificate using an existing key.
J.C. Hornbeck | Manageability Knowledge Engineer