Instructions
Download the "StarCraft" mod you wish to install. You can find pre-built mods at many "StarCraft" fan sites.
Unzip the downloaded file using a decompression program such as the free 7-Zip and place it on your desktop.
Double-click the mod to launch its installer. Follow the on-screen instructions to begin installation.
Select the folder that contains your "StarCraft" installation when prompted. Install all mods to your main "StarCraft" directory, usually located at "C:\Program Files\StarCraft\."
Click the confirm button on the installation window once you've chosen the correct folder, then wait for the install to complete.
Open "StarCraft" by double-clicking its icon to see your game mod at work.