Now, reader Zoega has written in with a few tips:
Just FYI, I've manually extracted and installed the new Intel UDMA drivers on W98SE BP6 (366mhz oc to 583mhz) with HPT366 1.21 drivers and it works great so far, well 24 hours.... Have run some extensive disk usage, copying and moving files, and running programs simultaneously, no probs whatsoever. The system "feels" faster than before, have no older disk benchmarks to compare with.So it looks like some folks are seeing success by circumventing the installer. Also, if you need the INF utility, grab it here.
One needs to first install the Intel® INF Installation Utility prior to installing the Intel® Ultra ATA Storage Driver. Then run setup like this on command line: SETUP -A -P c:\directory to extract and then one have to manually update each controller from system panel.
I got a rundll32 error when trying to update the Bus master Ide controller the first time but I restarted and then I could do it without an error.
Unfortunately the HPT366 isn't seen by the Intel utility program but when I use Sisoft Pro and check the Scsi module hpt366 has two entries, one for each UDMA66 and the Intelata driver has two entries, one for each IDE UDMA33.
Of course, messing with UDMA drivers not specifically intended for your hardware may leave you with a fried hard drive or a nasty rash. Downloader beware.