you may prefer to make linux live cd/dvd/usb stick instead. you download an .iso (system and installer image in one) of your chosen linux system, ubuntu based distributions would be easiest to start with. burn it to the required media, then boot the media using bios.
from there you can run it using ram and media, not hard drive.
check the computer is functioning properly though first, fans, temperatures (install psensor), graphics.
dont touch the files on the hard drive (as can be done from a file manager GUI for example), you dont want to break the computer for anyone else.
you do not have to install to the hard drive to use them. when finished with your linux session, shutdown through the software, then remove media.
if you want to preserve some settings between linux sessions, then buy a 4-6gb usb stick, a linux friendly and fast one if possible. use unetbootin to make it bootable with your chosen linux distribution.
stay with light systems if you want better performance, because read/write with external media is slow.
if you want fast, you could try puppy linux precise, its odd, and limited, but if you want to do geeky coding or whatever, i suppose it would be fine. the method it uses for 'live' mode is different from other systems. for puppy you need to make a cd/dvd, boot it, then choose to create a usb stick.