My friend Heiko Rabe wrote this Plugin, which shows all system relevant data of a WordPress intallation. It's a pure information tool, you cannot change any data or settings. The Plugin shows 4 tabs with information about the "System", "PHP" version, some "WordPress" functions, constants and "Database".
The Plugin works with WordPress 2.7 or higher. It will be published on the repository of wordpress.org soon, but if you need it immediately, you can download it on Heiko's website (Plugin is in English, the post is in German).