Thanks for your good wishes, folks... that's really in the spirit of DC!
I didn't really expect or need to destroy things to a standard that would leave GCHQ or the CIA bamboozled, just to stop cleverclogs with Recuva or something freeloading on my registration fees. I uninstalled everything I had paid for with my own money, either using Total Uninstall (where I had remembered to use it to install in the first place), or the progam's own uninstall, and shredding the directories and files that contained registration keys with Eraser. I found a portable version of Eraser on the Eraser site itself without going to PortableApps. I left everything that was free anyway, or bought by the company, and left all the matching data files. Then I went home, intending to do something like f0dder's second method on my last day. Unfortunately I did an uninstall too far, as XP wouldn't boot, complaining that "hal.dll" was missing. So that was that. So much for mindlessly saying Yes to all uninstall prompts... The IT guy had already told me that if they re-used "my" PC he would have re-imaged it anyway, so I probably did enough (one way or another). Not that he's likely to any time soon, as the company has laid off so many people he's already got enough surplus Dell boxes to build a garden wall. I told him about the failure to boot, "don't you just love Windows." He, who spends his time supporting Windows and Unix systems, told me he doesn't use Windows at home, but an Apple Mac! Paraphrasing: "It just works, and you don't get viruses."

Thanks again...