Now here's the problem: I tried to reinstall an unexpired downloaded trial version of Panda Anti-virus. Just as the CAB files finished being extracted to WINDOWS\TEMP, the opening screen of the Abi Word install routine came up and it became clear that the computer was now ready to install Abi Word instead! I got out of this bizarre situation safely.
On moving the Abi Word download, setup.exe, to a different folder, the Panda install problem disappeared. When I renamed it as AbiWordSetup.exe and left it in the same folder as Panda, the Panda install problem also disappeared. I imagine that some sort of cross-link had been occurring between a setup.exe file that's invoked during the Panda routine and the Abi-Word setup.exe.
As the evidence outlined above suggests that the name of the Abi Word download file was the cause of the problem, it might be helpful if you change it's name. Why not something with AbiWord" in the file name - at least then everyone would know what software they are dealing with, and the file name would at the same time have promotional value.
Anyway, thanks for a nice little editor - now that I know about you, I'll keep an eye on your site and see what further things develop. In the meantime, I'd appreciate a reply as to what you think of the above.