Note: There are different ways and softwares to customize your win-environment but I'll talk about CustoPack tools since it's the easiest to use.
First a preview of one of the many ways your windows might look like after:
Preview one: My Computer
Preview two: Notepad
Preview three: MS Word 2010 Starter
Preview four: Google Chrome
I would have included the taskbar but it's mostly hidden and I didn't customize it much. There's a bunch more awesome customizations available. I'll show you how.
1. Install CustoPack
Download it here. While downloading proceed to step 2.
2. Choose a Theme
Browse the themes here. Once you find one you like. Download it and leave it for now. My theme is Adaigo Some themes modify just a few elements while others customize everything from the logon screen to the taskbar and adds a nice transparency or changes most of the folder icons. I also suggest Elune theme.
3. Run CustoPack and Install a Theme
Choose "Choose a CustoPack"
You'll be able to see a bunch of themes you've downloaded. Click one and it'll ask you to install the theme. Spam the next button until the installation finishes. It'll need a restart. So do it.
It's done. You'll see that the your windows environment has been awesomized (Well thats if you didn't choose the damn twilight theme).
A few more things you can do:
4. Modify RocketDock
Some themes come with RocketDock which is a Mac-like object/app launcher. I'll make a more in-depth customization tutorial for it later.
5. Modify Desktop Wallpaper and Logon Screen
If the default wallpaper doesn't suit your style go ahead and change it. You can choose "edit current CustoPack" and it's pretty easy from there to change the Wallpaper and Logon screen.
That's it! Pretty easy and straight forward. Oh sometimes CustoPack crashes, just relaunch problem if that happens. Have fun!