Later versions of MS Windows includes a build of MS Paint/Paintbrush that will open JPEG files. Just drag the file you wish to view to the MS Paint icon on your desktop and the program will open and show yo the picture. Of course the later versions of MS Windows include the "viewer" which should give you a preview of the picture shortly after your cursor lands on it.

Cerious Software markets a program called ThumbsPlus that will open many different picture file types, perform editing operations on them like cropping, and allow you to save them back to your drive in a number of different file formats. The program can be downloaded as a deliberately "crippled" evaluation copy, that allows you to use it for a bit and see if it will do what you need before you pony up the registration fee for the complete version.

Dave