Hi Glen. I'll try to help with as many of your problems as I can understand. First the file associations. When you installed Photoplus it assumed that you waould want it to open all your graphics images. If you don't want it to do that, you need to reasscociate the files with anothre application (I have associated my image files with IrfanView which is an excellent free image viewer). In my Windows 98se system I find a file of the appropriate type such as .jpg, shift right click and select "Open with". In the list of applications I select Iview32 (you choose whichever application you prefer), and ensure that the box for "Always use this program to open this type of file" is ticked.
If you save an image as bmp it will be very large. It will have to fully describe every pixel of the picture. jpg compresses the file so the pixels are described with respect to there neighbours with other tricks to make the file even smaller.
For e-mailing you have to decide what the recipient will do with the picture. Unless it is to be printed as a high quality photograph it is best to resample it as a lower resolution picture or use a more severe jpg compression. How you do this depends on the software you are using. IrfanView has a very simple resampling utility that will let you reduce the number of pixels in the picture.
When you save your pictures, often the dialog boxes have a window for the file name and another for the file type. It sounds like yours doesn't want the extension in the file name box, ie the file name will be mypicture and the file type will be jpg. If the file name is mypicture.jpg it will add another .jpg when it saves the file.