Well I did it, I am now - ta da - running on Windows 7. I did a clean install onto another drive, which went amazingly well, and am now in the process of installing applications and copying over data. I'm sure this is going to take a long time and there will be all kinds of niddly things which don't work and hassles. And I'm sure I will ask myself more than once what problem exactly I was solving by doing this. But... I had reached the point where my Windows XP system needed to be re-installed anyway; cruft had accumulated to the point where the system was slow, the mean-time-to-reboot was about one day, and all sorts of stuff had stopped working or at least stopped working right.
The install process was fast and smooth, and "everything" worked right away as far as the hardware; somehow all of my laptop's devices were detected and connected. This includes stuff like the network card, WiFi, USB, audio, trackpad, power management, etc. - all stuff that in the past I would have been worried about, as being manufacturer specific instead of generic. That was a great thing.
The system feels "snappy"; I don't know if we give Win 7 the credit for this, or if it is just the result of a clean install, but at least Win 7 isn't slowing things down dramatically. I installed Office 2003 and Sharpreader and Citydesk and Photoshop, so I'm able to blog (!), and have a longish list of other applications to install and configure. And of course I am keeping a careful log of all changes so I can fall back if necessary.
Precelebration is the root of all failure, but so far, so good...