I just downloaded and installed the 2.6 version of WordPress. Got past the step where it creates all the tables and you are supposed to log in for the first time.
The problem for me was that the siteurl and home entries in the wp_options table had been incorrectly setup, in my case it was "http://myhost:81?step=2", how this happened during the config process I'm not quite sure.. but it resulted in the login page wanting to post to a url like "http://myhost:81?step=2/wp-login.php".. which doesn't play nice with IIS trigging a 405 error.
The page you are looking for cannot be displayed because an invalid method (HTTP verb) was used to attempt access.
HTTP Error 405 - The HTTP verb used to access this page is not allowed.
I searched around a bit and didn't find the solution, so i'm adding this in hopes it will help out the next person.
Ended up just editing the values back to something acceptable directly in MySQL Administrator and it fixed the issue right away.