Open the start menu, click All Programs, click Accessories, then Paint. Here's where you will make some art!
Step 2: Bring the art out of you!!! (Kind of)
Magnify to 8x, then make a small pattern of whatever you like in the top left corner.
It can be simple to very complex. The pictures show some examples.
Step 3: Make the white box smaller
Click the corner of the white box (a very small blue box) in Paint to make it smaller to fit your extremely small pattern.
Step 4: Save your artwork
Click File, then Save As, then choose what to call it.
Step 5: Make your picture the background
Now return return to your desktop, and right click it, and choose Properties. Click the Desktop tab, and click Browse. Find your picture, and click Apply. It should now look cool... or ugly, depending on your liking.