XP on my MAC

Hi Guys

I have just got a second hand mac with xp installed on it. When i boot it up it goes straight into xp. I want to reinstall either ubuntu or windows 7 but i cant get it to boot of the cd roms.

Ive tryed holding down C on startup with boot disk in but it goes to windows xp safe mode. Also i have tryed command+option+O+F, shift, option but it dosent seem to to matter what i hold down it either boots xp or goes into the xp safe mode choices.

Thanks for any help

Oh yes i have zero xp with mac's

Boot holding down the Option Key.
Boot back into OS X, put the OS X install DVD in and run the installer from there.

If there is no Mac Boot, sorry can't help.

Ive tryed holding down the option key and it goes straight into xp safe mode options

What happens when you reboot and hold down the T key?