So far I have:
downloaded Ubuntu 12.04.4 LTS from the site.
Converted the ISO file to IMG. (I used Unetbootin, I'm not completely sure I did this right.) I selected disk image, ISO, and browsed to find my Ubuntu ISO file. I saved it to a 4 GB flash drive.
I put the flash drive in my parents' old HP Pavilion. I rebooted, and hit escape to get to the boot menu.
I could see my flash drive as an option. I selected it and hit enter.
--And then Windows XP just starts up like always.--
Even though I select my flash drive from the boot menu, Windows XP loads up. I'm not a computer wiz, and this is my first attempt to play around with Linux. I heard using a cd is easier, but the cd drive on this pc is toast.