After several days of struggle, I am still unable to get a triple-boot disk set up on my Fujitsu Lifebook S6510. The first problem that I ran into was that the Windows installation disks I have are actually "recovery" media from Fujitsu, and as such they will only recreate the factory-delivered configuration, with Windows (Vista or XP) in the C: partition, which they assume is the first readable partition on the drive. That's no good for me in this case, as it causes one to install over the other, and I haven't found a way to trick the recovery procedure into installing in any other partition.
My brother gave me what should have been a good tip, when he suggested using Acronis True Image to back up my running XP partition, and then restore that to the second partition of the new drive. Rather than do exactly that, though, I also have Acronis Disk Director Suite, which knows how to copy partitions, so I figured I would use that to copy my current XP partition onto the new disk.
Unfortunately, try as I might, I couldn't get it to work. It was tedious to get the partition copied, because Disk Director seemed to have a very different idea than I did about where it was going to make the copy to, and where it would get the necessary free space from. Once I got it copied, it would not boot. One of the more amusing permutations was when I first installed Vista, then copied XP into the next partition, and finally installed Ubuntu into the third partition. Ubuntu (Grub) correctly saw that there were two bootable Windows partitions on the disk, and both Vista and Ubuntu booted correctly, but when I tried to boot the XP partition, it actually started to boot Vista but then complained that the boot info was corrupt, and asked if I wanted Vista to fix it for me. Sigh.
Having read most everything I could find on this subject on the web, I think a major part of the problem might be the fact that my Vista and XP partitions both think that they have been installed in C:, so whichever one of them is actually not in the first partition on the disk still tries to use that partition when it boots, and that causes confusion and failure.
I suspect that if I had actual Windows install media, rather than these limited "recovery" disks, I would have more success. Maybe. I'm not done trying yet, though...