Sup /g/. Let's talk about tinkering projects.

Once upon a time I made a stab an Linux, but gave up when Windows didn't play nice with the dual boot. So now I have an idea. I want to learn how to operate entirely from a command line interface, so I intend to buy an old Thinkpad off ebay and install some light linux build on it.

My questions are, what flavor of linux is the lightest build whose shell operation will let me take the same knowledge to real desktop builds, and what kind of processing power will I need to run it?

pic related, what I'm thinking of running it on