Hi Peter,
Thanks for the plugin, I've just installed it in my blog, nice and easy. :)
Just one little thing: if you want your plugin to be XHTML 1.0 compliant, you should remove the language='JavaScript' bit.
Also, and this is also a minor detail, you might want to add a config option to display or not the (*) next to required.
Just one more thing (how annoying can I be!): the button to submit this comment says 'Save New Post', which is a bit confusing I think. I hope I'm not actually creating a new post, I just clicked on the 'Reply to Post' button.
Thanks again for your great plugin!