You'll have to read the html source of the website and look for rel="nofollow" where the comments are. You can view the source code by pressing Ctrl+U in Firefox, don't know the shortcut key for IE.
Well yeah, I guess I was so used with the shortcut key that I forgot about right clicking. If you put it this way, you can also choose "Page Source" from the View menu
you can also use a plugin for forefox called SEO for firefox...it labels nofollow links bright red. saves a lot of time
I found a blogpost regarding it...rare post on bloggingtruths.com/technology/how-to-identify-that-a-blog-has-nofollow-or-dofollow-comments copy-paste d link