just take a screen-shot and then crop it in some program
to take a screen-shot - press Print Screen (Its in the top corner of your keyboard above the insert key. = well usually)
To put it in any program capable of cropping - open the program --> if your using paint goto -EDIT -> Paste (or press CTRL+V on your keyboard.) If your using photoshop or fireworks goto -File -> New (or press CRTL+N) select clipboard in the drop down menu and press OK. Then follow the instructions for paint.
Then to crop the pic goto the crop tool. In paint this looks like a box with dotted lines. In photoshop and fireworks this looks like two right angle interleaving to create a box in the middle. Then select the area you want, once you've made your selection double click and voilà! Your masterpiece!!
Save the file, (I'm sure you know how) --> Use as avatar on footprint friends --> Be happy.
Theres so much pollution in the air now that if it werent for our lungs there would be no place to put it all. ~Robert Orben