Windows XP

SevenVG Refresh
Vishal Gupta has done a fantastic job with this theme. It’s simple to install, looks great, and features both normal taskbar buttons and iconized mode.

Windows 7 Complete
User DopeySneezy calls this one Complete, and he’s not wrong. Includes Windows 7 style system properties, display settings screens, and more.

Seven Remix 2.0
Niwrad Soft recently updated his theme, and it’s even more convincing than V1.0. 

Windows Vista

Windows 7 Essentials Pack 
Another Deviant Art theme – this one by Ka-Booka includes just about every UI tweak you could possibly want to make Vista look like Windows 7 – even a Windows Media Player 11 mod, though some of you may choose to skip that one based on previous feedback about the new look.

Some more links:

Windows Seven(7) Transformation Pack is here

Windows Se7en (Vienna) Transformation Pack is here

Winmatrix lists 5 different options here

Technoworld also lists their Top 5 here

AskVG has a How To Guide for converting without the use of a transformation pack. The instructions are here

source: LifeHacker

Check the video below for a full feature walkthrough.

Here is the creator of BumpTop, Anand Agarawala demoing BumpTop at a TED conference.

With its 5 fascinating eye candy layouts, FoxTab takes the tabbed-browsing experience to a new level.
FoxTab enables grouping, filtering, closing and switching between tabs quickly and easily.

FoxTab is configurable, so you can easily tweek and adjust it to fit
your personal preferences (see more details below under “Advanced Details”).

For launching the FoxTab interactive panel just press Ctrl-Q (customizable) or click on the FoxTab icon located on your browser toolbar.
You can use the mouse wheel and the blue arrows to select your desired tab, or alternatively, use the keyboard Left and Right arrows keys.
With the interactive panel you can also filter tabs using a TextBox by pressing CTRL+F or group pages that were fetched from a common domain.

For quick tab switching press the Ctrl+Tab keys (also customizable) and the FoxTab interface will be displayed immidieatly.
Keep holding the Ctrl key, and press Tab in order to agility switch between the opened tabs of your browser.
(The same as you do with the Alt-Tab keys when switching between windows in Windows XP and Vista)

If you like to switch tabs without launching FoxTab, simply press and release Ctrl+Tab.
The selected tab will be the succeeding tab or the recently used tab (depends on a user-defined preference).

Installed the Windows 7 Beta and want some tips and tricks? Here you go:

Dock The Current Windows To The Left/Right Side Of The Screen

Press the Windows key + Left/Right key to dock it to the left side of the screen.

Shift The Window From One Monitor To Another

If you are using two or more monitors, then you might want to move the Windows from one to another. There is a very simple way to do it. All you have to do is press the Windows Key + Shift Key + Left or Right Key, depending on what monitor you want to move it to.

Custom Power Button

There is an option to replace the “Shut Down” button with another action, if you rarely shut down the computer, but you more often restart it or put it on sleep. Right click the Start Button, go to Properties and choose the ‘Power Boot Action” to do whatever you want, from the given options.

Missing Applications

Mail and a few other features are missing on 7. You can get them back by downloading Windows Live Essentials to get Live Photo Gallery, Mail, Messenger, Movie Maker, and other features from here.

Control-Alt-Delete

If you like using ctrl+alt+del but want only the task manager to pop up, try ctrl+shift+esc. 

Get Quick Launch toolbar back

Right-click the taskbar, choose Toolbars / New Toolbar

In the folder selection dialog, enter the following string and hit OK:

%userprofile%\AppData\Roaming\Microsoft\Internet Explorer\Quick Launch

Turn off the “lock the taskbar” setting, and right-click on the divider. Make sure that “Show text” and “Show title” are disabled and the view is set to “small icons”.

Use the dividers to rearrange the toolbar ordering to choice, and then lock the taskbar again.
 
Remove The Sidebar

Windows 7 doesn’t seem to feature the sidebar anymore, but it still exists and runs in the background, being launched automatically at startup. So if you want to get rid of it, there are two ways. The easier one is to press the Windows Key, type MSCONFIG.EXE, click the Startup tab and clear the Sidebar box. The hard way is to press the Windows key, type “regedit”, find and delete the registry key at HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run. This can save you some RAM consumed with no use.