I just did a fresh install and everything seems to have worked fine. My admin pages work great, I can post, I can view the site -- I just can't get comments working. I don't use permalinks and I don't have Pop-Up windows blocked. In fact, I've tried on two different computers using four different browser versions.
The only clue I can offer is this: I first installed the files into a subdirectory (/blog) but then deleted everything and installed again in my main directory. I ran install.php for the first install but I didn't run it again for the fresh install (wouldn't let me cause the SQL database had already been configured). I deleted all references to the subdirectory in the Admin pages.
Any ideas how to get comments enabled?