So.. the other shoe drops.
Windows XP works perfectly fine with a laptop that has a Thunderbolt 1.0 port (the mini-display port kind).
And at least when the HP Thunderbolt Firmware modification too is used to disable the "Only Certified for Windows" Thunderbolt port block.
Windows XP works fine with the Apple Thunderbolt to Firewire adapter.
I am not talking about using Apple hardware with Bootcamp. I am talking about using HP hardware running Windows XP Professional (and its probably not specific to "Professional").
The one thing different between Windows 7 x86 32 bit edition and Windows XP x86 32 bit edition when setting up a Thunderbolt connection is that after its hot plugged into the Windows XP system, it requires a reboot to start the service setup for the PCI bridge that is detected, until then it will have a Yellow Warning cone in Device Manager for it.. after it reboots it will finish enumerating and finding the OHCI port on the other side of the adapter.. this kind of makes perfect sense for the way that Windows XP does things.
On the laptop I have the ACPI HAL works for Windows 7 x86 32 bit, but does not for Windows XP x86 32 bit.. I had to use nLite to shoehorn the AHCI device drivers into the installer, make a .iso image.. and used an IODD external CD/DVD drive emulator to boot from the .iso image to start the installation.
When it got to the F6 additional device driver step, I used the undocumented F5 to select the specific HAL. This had the side effect that ACPI can never be used to finish shutdown in Windows XP.. and I did try all the other HALs.. but only Standard PC (legacy support) worked on this particular laptop.
Until I selected a specific HAL it would always shutoff after the F6 step and not complete XP installation.
Once I bypassed the autodetect of the HAL and continued the installation process.
I connected a Canopus ADVC-55 to the Apple Firewire adapter and it was dutifully setup and the Autoruns service of Win XP offered to start Windows Movie Maker to capture video.. which worked as expected.
In any event, the Movie Maker captured video also captured sound and imported it into the Movie Maker application for editing.
This particular example of using Thunderbolt 1.0 with XP on an HP laptop is rather unique in that at the time the laptop would have been over $1500 in 2012 dollars, so not many people may have tried it.
What stands out as very interesting is that while Thunderbolt has a firmware layer, it is independent of the general operating system. Once configured with tools for other operating systems it can be used with any operating system. To all operating systems it just appears as a hot plug PCI bridge device, any scanning of the other side of the bridge is at the discretion of the operating system once the port is in use.