1: Take a screencap of your desktop.
To cap a desktop:
1) Press "Print Screen" (prt sc) button
2) Open your graphics programme of choice
3) Press CTRL + V
4) Save image as a JPEG
2: Upload the screen cap to your image server.
3: Post your cap in YOUR LJ along with these instructions.
I know, I'm so "old school" with that background!