>If I knew how I wouldn't have asked.
(If 98 uses a different extension, change it to theme before you start.)
You can double click on the file. This also works on *.msstyle. OR...
Settings (Control Panel)
Display
Themes tab
click the down arrow on the Theme box.
select Browse... at the bottom
browse to where the *.Theme filles are.
Of course I don't know it it will work!
Or use the Desktop tab. There you can select the wallpaper, or browse to it. select Customize Desktop... There you can change the standard desktop icons.