vista and xp on the same hard drive

i have read William Wilson's steps to load 2 ops on to one hard drive
i have followed and completed up to the second step to install xp

i changed the boot sequence to boot from the cd drive it is all fine and the blue screen comes on and it is loadong the drivers for xp and as it is loading when it is don and windows would start for me to select which partition i will install xp

i get an error screen saying after windows setup a problem has detected and windows has been shut down to prevent damage to your computer

so what aim I doing wrong please help thanks