Actually, using cursor keys or a PC dance pad for the DDR clones have become quite popular. Look at these sites:

http://www.stepmania.com - Probably the most popular DDR clone out there. And its free and open source.

http://www.bemanistyle.com - A site that contains Sim files with the mp3 it goes to created by DDR fans.

There are other links to other DDR programs in them too. What you do for Stepmania, for example, is in the song folder, you create a main folder, such as "Music Downloads". Next, in that folder, you have a folder of the song you are gonna use in mp3 format, with the .sm or .dwi files (known as sim files) provided with them, which is the step pattern info, bpm, artist and song info, etc. I'm trying to parse it right now, but I'm not done yet.