i love the old windows 9x/me design. i think it is what made me love pixel art in general.
while there are a lot of icon, sound, or wallpaper packs online, there is not much of what i believe is the best source of pixel art in those old windows versions: the installers.
at that time, the installers and other wizards had pixel art illustrations on the left side of the window to generally illustrate the purpose of the wizard, and add color to this otherwise very gray window; especially the welcome pages at the beginning, often with very little more information than a title and a single sentence describing the wizard and asking you to click next.
those illustrations are quite detailed, more than the 16×16 and 32×32 icons. armed with one of my trusty ThinkPads running XP, eXeScope, Resource Hacker and Paint Shop Pro, i went on a quest to extract those illustrations, and any other interesting and rarely distributed bit of pixel art.
if you know of any good windows-style pixel art somewhere that is not yet on this page, feel free to contact me and tell me where you found it so that i can scrape it!