I've been having fun with hackerslab.org. It's a 'cracking contest', where you have to get through 17 or 18 levels. There's a tutorial here, in French (I hope that's not a problem for you ;) but only use it when you really don't know how to continue. It only goes up to level 8 anyway.
Time for some real work now.
If anybody has some information about living/working in and around Brighton,UK, I'd like to hear from you!