Not to worry—you don't have to register with Blogger just to post a comment here. When commenting, where it says "Choose an identity," just pick "Other" or "Anonymous."
The Other option allows you the option of adding your name and/or web site URL to your post you don't have to include either). The Anonymous option just assumes you don't want to include any personal information at all. In any case, you get a chance to preview your comment before posting.