ShellExtension is a real handy freebie for Windows users. Install this tool and it will add three new options to your menu when you right click on a picture file: convert, print, and thumbnail preview.
Converting supports most of the formats you will ever need: GIF, JPEG, BMP, PNG, TGA, PSD, TIFF, PCX, PCD, and a few others. The thumbnail option is particularly handy when you are in a file open dialog. Clicking on the thumbnail will open the image in the default program. For printing, there are no options, you get a centered image with the file path at the top of the page.