When you are extracting the file ( pulling the game folder OUT of the downloaded .ZIP FOLDER ) do you place it on you DESKTOP? If you DO, then click on the GAME FOLDER to see the files inside. When INSIDE THE GAME FOLDER that has been extracted FROM THE .ZIP FOLDER to your DESKTOP, just click the .exe file and the game should attempt to run.
If it says anything about a unity.dll, that means you probably MOVED THE FILE and when it runs, it can't find the files it needs to work correctly so it crashes.
If you get confused, try deleting the files for the Stewie game, and re-downloading to ensure you have all the files you need included in the .ZIP folder. This .ZIP folder is like the mothership, and the GAME FOLDER needs to be pulled from the mothership before it can be played, BUT, it must all be together to function.
Hope that helps.