I have a laptop with Windows 8 installed on it, it is the HP 2000 series. got it for Christmas in 2012. I inserted a CD with Ubuntu 12.10 in it (I got the CD before ubuntu 13.04 came out) and it was confirmed on another PC it worked, right now I'm downloading 13.04. and when I inserted the CD into this laptop, it didn't boot into Ubuntu, it went to Windows 8...
Windows 8 comes with a technology called "Secure Boot", which runs on top of UEFI and prevents a user from manually booting to another device. To get around it, you must:
Watch the screen right as your laptop boots up. You're going to hit one of the F# keys to get into the boot menu (mine is F12).
When you're in the boot menu, you need to tell the laptop to boot from the CD, and that should get you to the Ubuntu LiveCD where you can install or simply try out the OS.
Note: If there isn't a 'quick boot menu' or something similar, and you only see Setup (usually F2 or F4), you can still change your boot order from there. Just go into Setup/BIOS and look around to find the settings on boot order. Don't forget to change it back later if your bios doesn't have quick boot.