If you want to e-mail me, use ninety8-guy.  The full address would be
to add hotmail dot you-know-what to the end.

Here is my most comprehensive set of instructions to get WU working
for win-98.  There are a few other things that others have posted that
I should roll into this later.  But for now, try these:

First, I'm pretty sure you need to do the following:

1) add *.microsoft.com to your trusted zone list
2) enable everything (all actions) for the trusted zone
3) clear IE cache (including off-line content)

Then close IE and open it again.

Clearing cookies is something you can try, but it can be a pain if you
have some on-line settings (like banking, airline or frequent-flyer
website registrations, on-line forums, etc) so if you delete your
cookies you're going to lose all that, but I don't think that cookies
are involved in this WU problem.

Enter this in the address bar:

   javascript:navigator.userAgent

You should see this:

   Mozilla/4.0 (compatible; MSIE 6.0; Windows 98)

If you don't see that, then you have a wrong entry in your registry
somewhere (so that needs to be fixed).

Next, according to this:

http://support.microsoft.com/kb/817144

You might have an entry in your registry called "post platform".
Search your registry for "post platform".  If you have it, then read
the above MS kb article.  If not, then continue.

Finally, here is what will probably fix it for you.

http://support.microsoft.com/kb/193385

Navigate to your C:\Program Files\WindowsUpdate directory.

You will probably see a V4 and a Cabs subdirectory in addition to
maybe a few dozen files.

Delete all files (don't delete the V4 and the Cabs directory).  If
you're nervous about doing that, then make a backup directory there
and move the files into it.

So there should be no files in C:\Program Files\WindowsUpdate.

Go into the V4 directory.  There might be a few files there, and maybe
a temp directory.  Delete everything (including the temp directory)
EXCEPT for the file iuhist.xml.  Then go back into C:\Program
Files\WindowsUpdate.  MS says you can delete the Cabs directory, but I
just went into the cabs directory and deleted what was there (1 file I
think).

That's it.  Close all IE windows and then open IE and try Windows
Update.

Here's a few more observations:

I just went to WU and did the check for updates and viewed the items
to be downloaded and then cancelled the session without downloading
anything.

I then went back to WU and got the mac message.  I cleared the cache
and was able to get back into WU. I then exited and went back in, and
got the mac message, etc.

I did that a few times until clearing the cache didn't work.

So basically don't mess with it too much.  If you get in, then get
your stuff and don't play with it.

Does anyone know if there is an ActiveX cache?  There are references
to it on the net, but if anyone knows where it is, or how to clear it,
then please tell.   If something called an ActiveX cache does exist,
and if it's not cleared as part of clearing the IE temp files, then
maybe that's the answer to this WU thing.

Or maybe it's an active-x plugin that needs to be un-installed /
deleted?

One other thing.  Java cache?  Does WU use java?  What about jscript?
Does that have a cache?  How to you clear it?