A Windows Installer based application may fail to install when you have a bogus or empty environment variable present in your system.
Under NT-ish family OS'es, environment variables can be viewed by typing "set" on a console window (or control panel/system/advanced etc). Under 9X/ME, you have to open config.sys and autoexec.bat with notepad and check their contents.
Moreover, some installations made for Windows installer v.2 may not install at all under Win98 (but they will install under Win ME).
My link above for the cleanup utility seems dead currently, simply search for Microsoft Knowledge Base Article - 240116 which is the one referring to that utility.