what keys on your keypad do you need to reinstall xp, f6 or esc to boot from the cd drive. mine is escape key others might f12 or f7.
Anyway place the ubuntu into the drive and restart and pres the f key to boot form the cd drive and see, what happens.
Ubuntu should load up and from their there should an icon thats says install ubuntu onto your computer system, press on that, and follow online instructions, but be warned all your data will be lost unless you back onto external drive.
Im using Linux mint