The tool appeared to work successfully -- I've had very good results from nirsoft previously -- but the previous behavior remains. I'm still asked what to open this type of file with even after specifying the OPEN action in the tool.
It's ridiculous that Windows should behave this way - asking me what I want to open the file with, letting me make a choice, and then just discarding that choice and reverting to, of all things, Media Center.
(Parenthetically, is there a way I can at least get Media Center OFF of that list? It can't open anything in question.)
How could this issue have hung around so long without a solution from Microsoft?
I appreciate the compilation of links, if only as a litany of the things I've tried to get this elementary problem resolved. I resisted Win7 and hung on to XP until just a month ago. I'm beginning to regret upgrading.
I'm still running dual-boot. Maybe I need to go back to XP, as it looks like Microsoft still hasn't worked out the fundamentals yet in Windows 7.