This is easy. I cover it pretty extensively in my "Muvipix.com Guide to Premiere Elements 7".
With the frame you want displayed in the Monitor panel, click on the Freeze Frame button on the monitor panel (the camera icon) and then choose the option to Export.
There are number of options for formats to save the picture as under the Settings button. I recommend going in there and, under the Keyframe and Rendering tab, checking the option to Deinterlace. This will give you the best quality image.