Click on "Post a Comment"
Then you will get a popup like this:
Since I'm already logged into my gmail account, it automatically gives my information. If you're not logged in, it will ask you to. If you have a gmail account, you can do that. But if you don't, just go down to the circle that says "Name/URL" and open it.
You will now see this:
Here you just enter your name and, if you have one, the address to your web page. You can even enter your myspace page if you like. The URL space is optional for anyone who doesn't have a page, or anyone who doesn't want to share.