Open your wall and press Ctrl + Prnt Scrn. Then paste the image into Paint. Crop out what you don't need and save it as a .png. Then go to http://tinypic.com/?t=postupload and upload the image. Get the code for forums and message boards and paste it into your message. And before you can say 'pickles' everyone will be able to see your wall.
Instead of paint,if your on vista,type in snip it in start search bar,from that it enables you to save any part of screen you wish to save so you dont need print screen ,that then saves to your computer which you then take to imageshack.com to get the direct link for message boards,if your trying to edit pic and make it the right size for things like sigs or game profile pics then lunarpic will sort it