Well, since two of my podnahs have done this...

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.

( My desktop screen at work )