In Windows 98, find a file in Windows Explorer of the type you want to open. Press Shift + Right click ind in the list of options select "Open with". You should then get a list of the programs you have. Select the one you want to use. If you want the program to be permanently associated with that file type, then put a tick in the box to always use this program. As pj123 said Irfanview is an ideal program to view almost any type of image file, it is also very good for basic image editing, slide shows and batch conversion.
OK., so now I know where to find the "Open with" command, I need to figure out which programme to use. Is there a default viewer in Windows 98 or Office 2000? If I want to write them to disc and open them on another computer I obviously don't want to save them in something that won't be rcognized.
.jpg is an industry standard for image files. They will be able to be opened/viewed on any computer that has an image editing or viewing application. As far as I know all Windows O/S have "Paint" included. Even Word will open a .jpg
In windows 98SE On the "Open With" scroll down the list and select MSPaint. Now every time you double click a .jpg it will open in Paint. But to get a complete folder of jpgs as thumbnails you will need something like Paint Shop Pro or Photoshop or as already said Irfanview.
I think the default program is Internet Explorer, but for this purpose Irfanview beats it by miles. It doesn't matter what you use to view the files, unless you choose to "Save as" something different they will stay the same. Windows Explorer may attach a different icon if you associate the jpegs with another program, but that will only be on your computer. Anyone else will only see them as jpegs. Try Irfanview, I guarantee that you won't be disappointed.