Sorry - forget the ipconfig
I think it's unlikely that avg or malware whatever would create an either / or internet access situation - same for hijackers.
and if the mac works it's not port problems either
Back to ie6
In security settings is the reset to default option there?
do you have the option to uninstall the 5.5 to 6 upgrade?
That leaves the USB thingy
98 doesn't have native usb support (it's a sort of bolt on patch) and requires extra drivers.
you could try uninstalling/reinstalling the ISP software
and if necessary removing the USB entries in control panel
Only other I can think of.... if the bindings are kaput
I hate to use this as an answer (it's a cowards way out .... but 98 is a dim and distant memory ......)
it will at least prove a point.....
If you can go to
http://www.mozilla.com/en-US/firefox/
download firefox and install on your 98 machine
It's a large download (5.8mb) ... and I know you have difficulties d/l ....
but it would be interesting to see if this does the trick