Hi there,
I see many interesting 'alternative' projects that customizes win9x here, sho here's my idea: a patch that gradually substitutes Windows 9x components by open source ones.
Starting from simple 'components' (such as fonts, icons, shell, embedded apps, etc) to the deep core (memory manager, kernel, etc).

Here are some interesting links (for the purpose):

win-clones
ReactOS
E/OS LX

icons/desktop
Tango Desktop Project

fonts
DejaVu fonts
MgOpen typefaces
Free UCS Outline Fonts

shells
Litestep
BEOSWin
DarkStep
Blackbox for Windows
SharpE
Serenade
xoblite
GeoShell

applications/tools
Check my Untested (open source) software list @ ReactOS' wiki