Okay, lately I've been seeing to many people with extremely bland desktops and it really hurts my heart, so i present you with:
VectorKing's Ultimate Guide To Desktop Customization
Table of contents:
Section 1 - A desktop background
Section 2 - RocketDock
Section 3 - Rainmeter
Section 4 - Windows 7 Bonuses.
Section 1 - A desktop Background
The first thing we need to determine before finidng us a snazzy desktop background, is our monitor resolution, this can be checked a number of ways:
Now that we have determined what your screen resolution is we need to find a awesome desktop picture to fill your moniter with.
I personally recommend the website:
WallpapersRoom
Head over
to the website and select the resolution you found from the following drop down menu on the right:
once you have selected your resolution you can choose how the website displays it's selection of wallpapers, you have 3 choices:

I recommend you tell it to display the "most downloaded" because they are usually the most attractive wallpapers.
now just sift through..
XP
choose one wallpaper, click on it's thumbnail press download and click on the resolution you want, then right click and press "set as desktop background"
windows 7
choose all the wallpapers you want, by clicking on there thumbnails, pressing download and choosing your preferred resolution, download all the wallpapers you want into a folder.
now right click on your desktop select personalize, and then press "desktop backgrounds". now that you have done that press "browse"

and select the folder you downloaded all your wallpapers into, now you have some options:

you can set it to change your wallpaper every certain amount of time, and/or shuffle.
Section 2 - RocketDock
In section 2, we are going to be talking about the application RocketDock
first download rocket dock from here and install it.
once you have rocket dock installed you should see a beautiful mac like dock at the top of your screen. you can customize rocket dock in many ways, first thing we are going to change, is the theme.
if you want to go all out steve jobs, you can download the Leopard theme
for your rocketdock, once downloaded put the files (once extracted) in:
C:\Program Files\RocketDock\Skins
and for 64 bit
C:\Program Files (x86)\RocketDock\Skins
to change the theme press the dock settings icon on your dock, press the paintbrush icon and choose the theme from the drop down list:

Now that we are finished with the theme, we are going to move on to a Awesome docklet called Stacks. stacks imitates the stack feature in leopard.

to download Stacks, got to here download it, and insert it here:
C:\Program Files\RocketDock\Docklets
now to change the icons on your dock, you can use any standard png icons simply search deviantart and you will find massive amounts
to change an icon in rocket dock, right click it choose icon settings, add the folders where your downloaded png icons are with the plus icon, and choose from there.
now we have a super snazzy dock like this.

now we are finished with the rocketdock section.
Section 3 - Rainmeter
Have you ever used widgets or gadgets? well rainmeter is that, multiplied by a hundred, its a fully functional fully customizable desktop widget like app.
This is what rainmeter does to your desktop:

download the new rainmeter here
once you have it downloaded, you can use the built in gadgets that it comes with, or you can download tons tons more from here:
Most Popular Rainmeter Skins - Customize.org
Here are some rainmeter skins I personally recommend:
Lexis
SuperCollosal
Hud Vision
*How to install Rainmeter skins*
Unzip whatever rainmeter skin you downloaded, transfer the unzipped files into the "Skins" folder in your rainmeter program files, now right click the icon of the teardrop that is on your windows system tray choose configs and then choose your skin.
If you rainmeter skin still has not appeared, press "Refresh"
*How to install Rainmeter skins*
here is my desktop with some rainmeter.
now we move on to:
Section 3 - Win7 Bonuses
using windows 7, comes with a few perks, one of them is the super awesome taskbar customization, head over to deviantart, and download
ClearScreenSharp to get the awesome look you have been waiting for.
now that you are done, sit back relax and enjoy your awesome desktop.!!
for more information on using 3rd party win7 themes check here