All programs Designed for Windows 98 have an uninstaller you can access from [Start] -> [Settings] -> [Control Panel] and double-click at the [Add/Remove Programs] icon. In the [Add.Remove Programs] window, select the program that you want to uninstall and click on [Add/Remove] button.
A program's uninstaller will remove its components and Registry entries, if properly written. If the program included extra subsystems, such as DirectX or QuickTime, their uninstaller will usually leave them for other programs to use. These extra subsystems should also have their own uninstaller.