Such a compassionate welcome to a new user: Delete, unanswered, my
first help request, then insult me. Clever support strategy.

Clearly, I'm off to a poor start. Let me try again.

How can I install WLP to the D:\ partition under XP/SP3? Fidelity's
install script, unlike that for ATP, gives me no choice of destination.

Try to keep in mind that it's often difficult to convey sentiment on a forum, so if you feel insulted by something I or someone else said, I'm sorry, but I think you must have taken it the wrong way.

Anyway, I don't recall seeing this question before, and, I haven't noticed the Fidelity installation not offering a choice for Destination folder until now. There's not much anyone can do about the existing installation choices for now, but I'll create a ticket at Fidelity to suggest adding a choice for Destination folders in future installations.

If I can find a back-door method to point an MSI installation to a new folder, I'll post it here.

Well, mainly for the purpose of posterity, this would be the way to force the target directory using the Windows installer (XP):

msiexec /i "C:\Documents and Settings\[Your Windows Login]\Local Settings\Application Data\Downloaded Installations\{AB88AABE-57F0-4FEC-A6D0-D31A2D8D75C9}\Wealth-Lab Pro 6.1.msi" TARGETDIR="D:\YourTarget"

... but it won't work for Wealth-Lab installations. The reason is because the installation has logic to determine the target directory for installations on a computer with a 64-bit O.S. So, even though you can initialize the TARGETDIR property, the installation overwrites it anyway. Consequently, the choice for a new target must be provided by the installation itself.

Naturally, programs are expected to be collected under Program Files (Windows way) so it's possible to change the folder location via a registry hack.

As an alternative, you might want to explore the symlink option i.e. set up a symlink at "C:\Program Files\Fidelity Investments\Wealth-Lab Pro 6" pointing to the actual location at D:. Look HERE and HERE; absolutely no guarantees of course as it's a workaround.

Thanks for the apology, symlink pointers, and for confirming my suspicion regarding Fido's XP installer.
The W7/64-bit version does apparently behave more reasonably and successfully installed WLP on D:\ for a
friend of mine. I'll try again when I move to W7, myself.