There are many "hacker wargames" available on the internet, occasionally I'll play on some of the text based servers to get a few jollies. I recently ran across a site called "Smash the Stack" that runs a handfull of text based game servers. These servers typically run a flavor of Unix or Linux and the goal is to advance through each level of the game until you complete all levels, or in some cases, root the box outright on your own. Basically, it's legal hacking, a chance to test certain skills and try and root someone elses server by problem solving (they typically frown on attacks that may kill the server and ruin the game for others).
Typically all connections are made over SSH, if you have a Linux machine you can use SSH from a terminal to connect and you can use the puTTY terminal emulator to connect from both Win32 machines and Linux machines.
If your interested in wargames or want to try one for the first time, go over to Smash the Stack and give it a go.