One way off topic question. Can you set up an unattended disk to work on 3 different home computers that each have their own different product keys or do you have to put in the product keys on each install making it not a true unattended install?
That's a tough question.
I have had a similar discussion on the German nlite forum and the general consensus was it's not possible.
I'm not so sure this is a final answer, however, it certainly does not work by simply adding three keys to your WINNT.SIF.
What I could image is that you create an exception for the finisher that would re-write the key to the registry after installation based on a specific hardware found only on one of the PCs (ie each one must provide at least one piece of HW that is unique).
Else I wouldn't know how to distinguish between the PCs.
What certainly does not work is auto-activation.
You either need to use a Corporate Edition of XP where you do not have to activate at all or you will have to do that manually after installation for each system.
You could, however, save the activation file and copy it over when you reinstall, but that requires exactly the same HW configuration.
Not entirely too practical.
Another idea is to simply use the same key for all three machines.
That's how it's most likely done in most businesses (obviously, if you have the Corporate Edition, you'd also make it fully unattended compatible).
After all, to legally use the OS, you only need to have a valid licence for each machine, and that is the only thing MS cares about.
You could even buy a licence without a CD and obtain that elsewhere, that wouldn't even be illegal.
Therefore, the key isn't what makes it legal, it's the licence - one for every machine.
However, unless you own a CE, MS will at least get suspicious on activation if the same key is used (obviously they couldn't know whether you own the licences or not...).
How you deal with that I cannot tell you, however, I have heared, using phone activation and answering "only one" to the questions on how many PCs you have installed will get your system properly activated.
Again, you NEED to own three licences for three PCs or this will be illegal.
If you do, it might be morally wrong but legally it should be ok.
Then again IANAL, so take this all with a grain of salt.