Installing xp on external hard drive ? Error

[Amank]

I buy an external drive to connect western digital firewire to install windows xp, I make a 20gb partition on the disk to install xp. being given that my system is operating vista, when I ve xp installed on the external drive, a message appears "the windows version is incompatible with your" so I dint installed xp on the hard drive !
how can I do this ? thank you for your answer

[opaper]

if you want to install xp external hard drive . you should rule in your bios,,,, is that boot on hdd1 or hdd2 .

[Aikonik]

install the bios to bring the cd from the demarrage,,after choose what you want to partition install Win XP, if it does not happen you have to return to the boot setup where it is shown on what must support from the demarrage the pc and then choose of the CD player or DVD the drive in the second after restart the PC .

[Dr. V]

thank you to respond as quickly:
when i put the CD does it launches in the start, I go into the bios and press f12 getting started the cd "no response"