I have been using Irfanview for the past 8-9 years to view, resize and clarify pix! It's free from irfanview.com. One thing you should all know about jpg files though is that you shouldn't resave the files from within a viewer program very many times because every time you do you potentially recompress the file and lose more detail. Good idea to know how your program works though. All the pro photogs save in .tiff format so they eliminate the potential to lose info from their pictures.
Fyi,
S.