Well, I have upgraded to WordPress 1.5.1 and all was well until you tried to post a comment. This was pointed out by David earlier today. The problem was in the index.php file. It had the following line:
require('./wp-blog-header.php');
Well, on the Dreamhost servers that was causing a fit. So, since I knew that the file would always be in the same folder as the index.php file I just altered the line to read:
require('wp-blog-header.php');
All I did was take out the ./ for the relative path to the file. I think it’s silly to have it there in the first place, but oh well. Now it works and you can post comments again.
Update: I’ve let the DH dev team know and they are looking into it.