HandySolo: AWESOME! That got me back, but only partially.
First, yes, the blog's URL was originally in /blog, but when I made the move I decided to bring it to the root.
Okay, so that part of it's done with, but something's still amiss. I recreated my htaccess file and set it back to 664 as the WP documentation instructs. That help me get to a post if I clicked on the recent posts widget.
But if I click on a recent comment, there's an error. Actually, this sounds related to http://wordpress.org/support/topic/132720?replies=2 which involves another blog I moved to the same host and how its categories are still screwed up.
I'm happy to carry on that thread over there if you like.
Again, thanks so much for the help you've given me so far. This is a major step forward as I've been struggling with this all day. :)