http://windowsphonehacker.com/articles/beta_release_lock_widgets_for_windows_phone-03-20-12

• Your device must be rooted. More specifically, the application needs root privileges. More info on that later. (That's good)
• The "debug" widget adds the last updated info to the bottom of the screen. This is useful stuff for testing.
• The widgets update every 30 minutes. This is due to background task restrictions.

Developer has requested we link to that page instead of direct download links. I have it on my phone now, Christchurch weather works and Bing Wallpaper is cool for the lockscreen, means it changes every day!

EDIT: This requires an unlocked phone, you can get this by having a Developer Account (free for students through Dreamspark), Chevron unlock or a Custom ROM (like the DFT ROMs). You also need ROOT privileges (custom ROMs automatically have this) and the developer will explain this at a later date