Okay, I've done it. I followed Gina's guidelines over here at Lifehacker:http://www.lifehacke...m-scratch-157578.php
and everything went amazingly straightforwardly.
Though I've followed the advice of creating a separate partition for my documents etc and OS/program files, I've never quite believed that this was useful: it certainly is! I didn't realise I would only have to reformat the OS/program files partition, so my data was perfectly untouched. I made an image of the data partition on my snazzy new 250gb Lacie drive, and for good measure dragged-and-dropped it there also.
Now, with a clear system, I am slowly working through the Belarc Advisor system profile and reinstalling the programs I elected to keep - less that half! I am installing each program with Total Uninstall, and I intend to use it every time I install anything, so that I can keep things as clean as possible. Even with this very select group of chosen programs for installation, I am finding that I want to dump some things - for instance, although I have re-installed WindowBlinds 5, a short search of available themes for it has left me very disappointed, so I am using the (to my eye) beautiful MS Royal theme.
As I expected, even though I had carefully prepared for this over a few days, I found in the end that I did miss one important thing: my Roboform data, which I thought was in the Documents partition, but must have been in C;/Documents and Settings/etc. That's a bit of a pain, but I will survive it.
What is really unexpected is the difference in operating temperature! I use Speedfan to monitor HD and system temp., and it has fallen significantly since I reinstalled. About two months ago, when my system repeatedly fell-over while playing Civilization IV, as well as constantly making a deafening noise, I took out the heat-sink and cleaned everything up, removing about a cats-worth of hair and muck from the fans and filters. At that point, it was running at 70-80 degrees C. I put everything back together, and since then it has run at about 48 degrees C, climbing over the past few weeks to 51-53 degees. Today, completely clean and only partially reinstalled, it's idling at 31 degrees as I type!
Thanks for suggestions and support on my brief odyseey into Reinstall Land.