Zorin OS is an Ubuntu-based Linux distro that attempts to be as much of a clone of Windows as is possible. I'd still say, if you really want a free Windows clone wait until ReactOS is fully developed, but Zorin is as close as Linux is going to get as of now.

This is the desktop.
As of this writing, Zorin OS is a near mirror of Windows 7. Thankfully no bastardized Windows 8 Metro crap.

Of course the Aero interface is non-existant because that would be a lawsuit magnet, but the taskbar is pretty much the same. You can pin apps to it (although it isn't nearly as streamlined as it is in Windows; you have to do it as if it were a standard quick-launch item), the taskbar or "panel" has a glow to it, and the desktop icons are all shiny and the size of school buses, just like Windows.

When you hover over an icon pinned to the panel, it highlights itself, much like it would in Windows 7.

The start menu looks pretty much identical, although the way application browsing works is implemented differently.

Zorin uses Nautilus Elementary to do the file browsing.