Hello. I just upgraded a rather messy WP 2.0 to WP 2.5.1, deleting all the files. The problem is that after the install I can't access themes.php and plugins.php. The only think I get on Firefox is a white page, on Safari I get "Safari can’t open the page because the server unexpectedly dropped the connection, which sometimes occurs when the server is busy. You might be able to open the page later."
Otherwise things seem to be working ok, there's no white page issue with posting new articles etc.