I've installed WordPress 1.5.1 and can't log in. I click log in with the right credentials and it sets the wordpresspass_ cookie then it redirects me to wp-admin/. There it performs auth_redirect() and redirects me back to wp-login.php where I started.
I've tried everything I've seen suggested in the forums / wiki but nothing works :-(.
If you want to try it, http://sirg3.homeip.net/~allison/ -- admin / temp01 for login info.
I've tested that other scripts can get / set cookies fine. http://sirg3.homeip.net/~allison/test-redirect.php (it sets the cookie, then sets the location header to test.php, then test.php reads the cookie).