Sorry for butting in here. What program do you use to view your pictures? You should be able to go to "Save As" and chose the format from a drop down menu. Sometimes, just changing the extension works too, eg: .tif to .jpg. If you want to post your pictures on line .jpg is great, but every time you open a .jpg file it loses some of its information, so if you need to keep your pictures for posterity you should save them in .tif or .eps format. Dont' know if this helped at all, but there it is! :)
Edit: If you don't have a picture viewer there is a free one you can dowload: it's called IrfanView and there are tons of sites you can download it from. You can change the extension, resize, lighten, darken and edit your pictures.Get IrfanView 4.0