Well, I had a look around, and see that this has never been addressed as a feature, and there is no way to easily empty the comments in moderation. Wow, of all things, I would guess this would be worked on.
You can do it via phpmyadmin with a simple query.
You have more to worry about than some spam comments, though.
<meta name="generator" content="WordPress 2.2.1" />
you need to upgrade your blog, youre way behind, and there are a whole box of security issues that have been adressed since that version.
Of all things, I would think that would be your priority.
I’m guessing you’re not using Akismet, which includes a “Delete all” button.
If you were and just needed help reviewing all the spam before deleting it, Akismet Auntie Spam would help:
http://userscripts.org/scripts/show/7037
