What do I need to convert/use 2nd comp?

[dareutwo]

I have this 2nd actually 3rd box just sitting here.
Instead of it simply collecting dust, I'd like to turn it into a computer I can use for development stuff... ie programming in php, databases (mysql) etc.

Basically I'd like it to be set up similar to my regular hosted box, but simply right here, so if I screw something up (which I do regularly) I can just reboot or whatever.

I won't be hosting anything or serving any pages to the outside world, just to and from computer #2.

Any help, advice greatly appreciated!