WinInstallLE is a program to generate MSI files. It requires that you set up a clean PC with only Windows installed, nothing else. You need another PC with WinInstallLE installed.
The program works by creating a snapshot of the PC before software installation. Then you install whatever software you want to get a MSI file for. Then you run the software again. It now compares the snapshot with the new state and creates a MSI file.
The program was freely available and distributed by Microsoft on the install CDs of Windows 2000. A later version was available for free for download from the web page of its creators. A commercial version is still available.
When I tried to create MSI-files for Firefox with this, I noticed that it's somehow unreliable. Often the files work, sometimes they don't. Although the PC was as cleanly installed as it can ever be. So I stopped using this and moved to AdvancedInstaller, later to WiX. They allow to precisely specify that the MSI-file should do.