Assuming that you're using a Windows PC, using the PrtSc key has now largely been replaced by the (much better) Snipping Tool that comes with Windows. To access it, click the Start button and go to All Programs > Accessories. Click on Snipping Tool, then drag a rectangle around the part of the screen you want to capture. Your image will appear in a new window. Go to File > Save As to save it as a jpeg file.