Windows Update V2 still fails, cannot install .MSI files

W2K multiboot system. (Windows ME and several copies of Windows 2000, only
one W2K system has Internet access and security programs.)

On advice in another Windows 2000 group, I let Windows Update 3.1 V2 install
itself so I could get some critical updates. I got them, but afterwards
*again* (same as WUP 3.1 V1) could not install any .MSI files. I'd click on
them but nothing would happen. So I tediously removed all MSIEXEC.EXE files,
ignored the whines, rebooted, and reinstalled Windows Update 2 so I could
install .MSI files.

AFAIK my system is fully patched. Why won't WUP 3.1 V2 work, and what can I
do about it? My whine: I don't want to go through this every time I want to
update my system.

--
Walterius