you used a digi-cam to take the pic right? And it came out huge!
See if your cam then has some options, make it save the pic as 1024x768 or 800x600 if you want some nice wallpapers, if you want stuff for posting trying 640x480 or 320x240.
If your cam doesn't have this option, get a drawing program, and resize it. I think you can do it in MSPaint, which is all all windows computer, but then again you'd have to save your pic as a bmp which i'm not sure if any digi cam would.