Found an old computer in the basement. What steps should I go through to get it up and running? Seems a previous tenant left a computer tower in the basement. It's from, at the newest, 2003.

I plugged it into power, hit the on button, and stuff whirred, and green lights came on. It doesn't have any cables, mouse or a monitor, and my access to a monitor will be limited to what I can borrow off friends for short periods (have a MacBook, if there's some neat trick to be able to use it as a monitor...).

What can I do to get this up and running (thinking of installing Linux or BSD) - what bits will I need to scrounge, what should I do to check that everything's in place hardware-wise etc.?

And secondly, what flavour of Linux/Unix should I install, and how can I go about making this thing useful beyond being a pretty neat geeky playground?

Basically, what's the ABC of going from pile of junk to functional in this situation?