Hi Megatop. I think you want to install aircraft as you already downloaded the files. Please read this tute first & follow the instructions carefully.
http://www.simviation.com/acinstall.htmIgnore section 4 as it does not apply to FS98. If you're using WinXP you won't need WinZip. If you still have problems post here again & try to explain what you don't understand.
It's easy once you understand the basic principle. Good luck.