
A group of people are developing an alternative shell to Windows Explorer AKA "explorer.exe" for Windows XP and Vista, called "Cairo." Unlike skin packs like Vista Transformation Pack or VistaInspirat which modifies system files, this just disables the default explorer.exe and enables it's own taskbar and explorer shell.
From the initial screenshots, it looks very promising. It just hit Milestone 1, so it'll be a while until the final version comes out. Since it's still being developed, the system requirements are not finite yet, but according to developers, they have said that any computer made within the last three years should be able to run it fine.
You can check out more details on the Cairo project at their website: http://cairoshell.com/

