Instructions
Unzip all the song files to a folder on your desktop. Song packs for Stepmania are compressed for easy download. They usually come in .zip files or .rar files. To unzip the file, right click and select "Unzip to" and then select a name and location for the new file. Name the file according to what songs are in the song pack.
Open the song folder to inspect the downloaded songs. When you download a song pack for Stepmania, it will include several songs. Each song should be in its own folder in order for Stepmania to read the files and group them into the appropriate song group.
Open each song folder and double check that each subfolder has a .dwi file, a .sm file and a .mp3 file. Each song must have these three components in order for it to work within the Stepmania game.
Copy the entire song folder by selecting the folder and pressing "Ctrl" and "C" on your keyboard simultaneously.
Navigate to the location on your computer where Stepmania stores all its song files. Stepmania songs are typically filed under "C:\Program Files\Stepmania\Songs"
Press "Ctrl" and "V" simultaneously to paste the new song pack into the main song folder. The next time you load Stepmania, the newly installed songs will be available under the name you chose for the file.