Here at work we I am running Windows 2000 and for the longest time the fact that tray icons could only have 16 colours has annoyed me for the longest time. With a lot of newer programs creating their icons to this high colour made the UI(User Interface) look really bad :(.
However to day I found a solution someone has patched explorer.exe for all service packs of win2k with a simple active x control. You can see it here. So right click with ie view for Firefox or if you are for some reason still using ie just click the link :P. But do please consider switching and enjoy your winXP style hi-color tray icons.