Thanks for the prompt reply. First, the "magic setting" was to change the FULL_SCREEN line in the FS9.CFG file (that gets hidden in the user's 'My Documents','App Data', 'Microsoft', 'FS9' file) from '=1' to '=0'. I don't know why this made a difference. MS support then had me 'reset defaults' in the FS9 trouble shooting menu. That restored normal sound function, but the program still crashes if I try to 'Customize Weather'. MS support then had me try a 'Clean Boot' but that didn't help. They then had me uninstall FS 2004, delete all FS9 related files, and reload the program in a new directory as well as download DirectX 9.0b (as opposed to 9.0a that comes with FS 2004). I did all this without loading your FSUIPC or PFC.dll modules to be sure that the problems had absolutely nothing to do with your excellent additions.
No luck. View mode changes now kill the sound again (that can't be recovered for any application until I reboot), and clicking 'Customize Weather' still crashes the program. At least I can fly successfully with your FSUIPC and PFC.dll as long as I don't change view modes from 'Cockpit' and don't try to set the weather. The later problem bothers me the most as I want to set cloud ceilings at minimums for instrument approaches but am unable to do so.
I'll let you know if I ever resolve these problems.