A .cab file is a Microsoft file archive format. It can contain a number of smaller files that are then compressed into a single .cab (cabinet) file, and these can include .exe files (Microsoft executable files). Normally, a .cab file is self-extracting, meaning that it runs any .exe files it contains as well as extracting the other files contained in it for use as resources by the .exe file. However, a number of different software tools available allow you to isolate and extract .exe files from .cab files, but one of the simplest is provided by Microsoft itself.
Download and install the Service Pack 2 Support Tools from the Microsoft support site (see Resources for link).
Move the .cab file you wish to convert to .exe to the desktop.
Click on the "Start" menu, and select "Run," then type "cmd" or "command" in the prompt, and click "Run."
Type "c:\documents and settings(username)\desktop" in the black and white command-line window that pops up, where (username) is replaced by your username in Windows. This will make the next command you run apply to the directory (your desktop) that contains the proper .cab file.
Type "Extract.exe Project1.cab /E" where "Project1.cab" is replaced by the name of the .cab file that you moved to the desktop in step 2. All of the files within the cabinet will be extracted to the desktop, including the .exe file.