Is nobody going to mention that Microsoft paint will already be installed on missprims computer and will do the job perfectly well. suggesting downloading a full featured graphics program to do one simple job is a touch of overkill IMO.
A lot of methods
1.Screenshot, then save as jpg. Some chat software has the function.
2.Microsoft paint: open the picture and 'save as', select jpeg...
3.Professional graphic software(Photoshop, fireworks, illustrator ect...)
4. Or a shareware image editor, serch it at www.dvd-creators.net