I think Win2k already had that. As far as I remember, the explorer sidebar, the white box with the colored line under the heading, already being HTML.
I loved hacking on that back then to customize my windows experience.
If you changed the colour scheme on Windows 98, none of the cloud images were transparent in Explorer (they assumed the background was white) so you'd end up with these weird clouds/sky fading into a white background and then a hard line into whatever colour you'd set your background to.
The desktop was very sluggish if you added an active desktop to it, as IE4 had to run; at least it was on my underpowered machine. Additionally it came with a screensaver that you could interact with, which was odd because normally moving the mouse dismissed the screensaver.
