Windows 7: AHCI : Enable in Windows XP after OS install

It can be very touchy.
It may be related to the manufacturer's hardware choices.

My friend got a new Windows 7 laptop for his work.
He had a problem with a chip programming device (USB), so we spent 3 days (in 2011) trying to enable AHCI.
We tried multiple methods outlined on various websites.
We could never get it to work.

Luckily it turned out my friend didn't need XP.
The external device that wouldn't work, actually had a problem with USB3 and not Windows 7.

I used the "slipstream the drivers into an install disc" method, when I reinstalled my operating systems last September.
I used nLite to create my new XP install disc.
It worked perfectly.

If your Win XP CD, does not support your Sata Controller, you will need to load drivers to uses at F6.
Load Sata Controller drivers with a floppy disk is the best way.
SATA Drivers - Load in Windows XP Setup on Dual Boot

We did try the floppy + F6 method.
We tried every method we could find on the internet, except making a new install disc, when we were working on my friends work laptop.
Nothing we tried worked.

Luckily it turned out that he didn't need XP anyway.

All of the various methods we tried, worked for some people, but they didn't work for others (like us).
I suspect that driver problems, hardware problems and/or user errors were responsible.