Hi Ann,
There is a difficult balance between image quality and file size for the web. When you converted your image to jpeg format did you use the jpeg optimizer feature? According to the reviews, Corel Draw is supposed to have a good one. You will want to use this process instead of the basic SAVE AS. When I save my images using an optimizer I start with 0 percent compression and see what the estimated download time will be. Then I nudge the percentage of compression up slightly until I get to a good balance of quality and download time.
Assuming that you have already tried the optimizer, you can try to slice the banner into smaller pieces and optimizing each of these individually. Sometimes that helps because you can use a lower percentage of compression on each piece. Try to use the same percentage in the optimizer process for each piece so that the pieces will appear as much alike as possible.
Hope this helps.