I managed to get this working and thought I'd post my results in case
anyone else can benefit...

Swapped PCI slots...had to try a couple of different
combinations...seems as if the Ethernet card and the USB Host
Controller card had some bad interactions...found a combo that seems to
work.

Found, downloaded and installed updated ALi drivers...manually
configured the ALi-related devices to use these.

After these two steps, USB devices are properly ID'd and seem to work
fine. The only exception is an external 80GB Iomega portable drive
that's formatted NTFS. Win2K3 detects the drive OK, but doesn't see a
filesystem on it. But I think I have found the answer to this last
snag.

My thanks to those who took the time to keep me from veering too far
off of the right track!