I was a bit bored a while back and wanted to put together something in PHP that was more than just a learning exercise, and ended up with a sort of game-challenge-site; it can be found here.
The only issue is that I didn't want to implement passwords for the sake of simplicity, but wanted a leaderboard of sorts (just to have something more to implement), which means anyone can continue, using anyone else's name - try not to, okay?
Since I'm nice (...), and since this would be a short page without anything else, I thought I'd put up solutions to all the current levels (not many at the moment...). It's up to you how long you go before using them...
Whenever I mention a page, it goes after http://fail.ikn.org.uk/ to make the full URL. Hints come before answers are shown. Yay, spoiler nesting. Click the headings to show the spoilers.