fun but way harder to learn than DDR, its played on a 5 (or 7 key - depending on version) keyboard with a record to scratch on. Still easier to learn than Keyboardmania though, where you have to play a full keyboard to music, that game doesn't even have a learning curve, its a learning wall!
I think the beatmania's in mame should run ok on a preatty fast machine, I've only played the first one in mame a whiles back. I used to use an emulator like Stepmania (DDR emu) or BandJam (DrumMania/Guitar Freaks) for it long ago where you put in music folders, can't remember what it was called. Anyone remember?