From the OLPC Forum: http://olpcnews.com/forum/index.php?topic=767.msg5302#msg5302
Topic: [Tutorial] Take a Screenshot and Transfer it to Your PC with a USB Flash Drive
December 26, 2007, 09:15:04 PM
1) Press alt + 1 on the keyboard.
Note: You can hold alt (the key with a diamond symbol) and then tap 1; then release both keys.
2) Open the Journal.
3) [Optional] In the "Anything" drop-down menu, select "Image".
4) Click the screenshot you just took.
(Your USB Flash Drive must be inserted by this point.)
5) Hover the cursor over the "Copy" icon (2nd from the right) and click the name of your USB Flash Drive.
Note: You can also drag the file to the USB drive's icon on the bottom.
6) Hover the cursor over the USB drive icon at the bottom, and click "Unmount".
7) When the light on the drive stops flashing, remove it and connect it to your PC for transferring as a normal PNG file.