Step-by-Step Downgrade to XP Pro from Vista Business?

Hello,

I've searched the Vista forums hi & lo regarding downgrading and only found
(1) references to the EULA regarding downgrades and (2) references to
computer manufacturers' warnings about downgrades. I understand the EULA and
my hardware is 100% compatible with XP Pro. That said ...

I have a new workstation that came with Vista Business and Downgrade Rights
( as choses during the system configuration on HP's web site ). So, here is
this system in front of me that has never been booted up into Windows. I
have, though, taken a ghost image of the entire drive as it sits with the
computer as it shipped to me.

I also have in front of me a Retail copy of Windows XP Pro Full installation.

Now, I've heard that I need to boot up into Vista and go thru all of the
preliminary gyrations with initial Windows Vista Business configuration.
Then, I was told to install the XP Pro CD - while in Windows - and I will be
instructed how to downgrade (which I find hard to believe 'cause how does
this retail copy of XP know about downgrading from an OS that didn't exist
when the CD was burned?).

I'd much prefer to wipe the disk clean and start anew so I can partition the
hard drive from the get go - booting into the XP Pro installation from the CD.

What are the proper steps, please?

And, what is the precise method to properly register and activate this
installation so it is noted that the Product Key on the machine for Vista
Business is referenced to the Product Key on the XP Pro CD?

Thanks, in advance, for your time and detailed explanation.

AlanB66