Welcome at MSFN Forum!
I have been trying to boot my XP Pro 32 bit in AHCI mode by implementing nLite, with numerous drivers and keep up coming up with the same problem.
To minimize the risk of an XP installation failure you should not integrate more than 1 driver into the CD.
This is what I recommend to do:
1. Restart the creation of an XP SP3 CD with integrated AHCI driver from scratch by using the tool nLite.
2. Integrate just the 32bit Intel RST Textmode Driver v188.8.131.526 WHQL.
3. When you get the nLite textmode driver popup, you should just check the listed "Intel® 7 Series/C216 Chipset Family SATA AHCI Controller".
4. Before you start with the OS installation you have to enter the BIOS and to set the SATA mode of the Intel SATA Controller to "AHCI" and to do the correct boot order (first bootable device: CD/DVD Writer.
If I use nLite and prepare CD with Win XP OS only and no AHCI drivers slipstreamed onto CD, then my 500GB Seagate HDD is recognized.
This only happens, if you had set the SATA Controller within the BIOS to "IDE" mode.
I read everything on the Index Page, and it appears my CD-ROM drive might be the problem, and I might have to purchase a USB Ext. CD-ROM drive to achieve my goal, however before I go out and spend unnecessary money, I would appreciate some feedback if this is in fact is the right diagnosis.
There are some optical drives, which do not like to run in AHCI mode (they cannot read the data of the CD/DVD), but I don't think, that this is the reason of your problem.
Try what I have written above. If the XP installation should fail nevertheless, please report here, what exactly happened.