I wonder MDGx, if you want to include the HTML Help files from the XP SP2 KB896358 patch and create an unofficial HTML Help 5.20.3790.2453 patch for Win98/ME/NT4. I've extracted the "SP2QFE" versions of the HTML Help files from the XP SP2 KB896358 patch, then installed them on the Win98 & WinME computers. they worked fine. they're actually a little newer than the HTML Help files found in the Win98, ME & 2000 versions of the KB896358 patches.
New HTML Help update files should be left alone the way MS distributed them, because each type of OS [9x or NTx] has its own specific functions/features, addressed within those DLLs/OCXs.
I'm aware that the XP files are newer builds than 98/ME files, but as far as I can tell those builds are different on purpose, and each target a specific OS.
This update fixes the same security bugs for all OSes, so there [probably] won't be any difference in functionality, no matter which build is used.
my 2 ¢