Thanks to Chris Pirillo for the tip: A group of programming enthusiasts has released an amazing desktop/shell replacement for Windows 9x and NT called LiteStep. Based on the NextStep/OpenStep user interface, and several clones for Linux, LiteStep provides multiple desktops, an easily configurable user interface, and dozens of themes that can make your system look even less like Windows. What's most incredible about this package is its size: The base download is only 700K! And installation couldn't be easier: Simply unzip the download, copy the directory to any location on your hard drive and edit one line in system.ini (actually, NT support is a little more difficult).
LiteStep is currently in beta, but the final version will be free. I've installed it on my Windows 98 partition and it works fine, without any bugs that I've seen. Still, since this is a shell replacement (it literally replaces Explorer.exe) I can only recommend this to power users that are comfortable really tweaking their system. It's a must-have.
Check it out at the LiteStep Web site