Hey!
You can find software at http://www.ketron.it/prodotti/dettagli.asp?sezione=5&idProdotto=-3
This is only for transfer in/out with the keyboard HDD.Nothing special with it.Also you will need a driver for the serial port.You can use ketronftp.zip if you use Windows 95,98,Me or a driver from Yamaha for Windows XP at: http://www.yamaha.co.uk/xg/html/software/s_serial.htm
The cable you can find at a local dealer, it looks like this: http://www.thomann.de/de/ketron_pckit.htm
If you are in Europe you can order there.With this cable you can do transfers to your keyboard,also you can access SD1 Synth like a normal Midi interface.That's cool.
For editing a midifile you'll need SD1 Mastering Studio from: http://www.soundcompany.net/sd1/mastering_studio/
This makes all the tweaking very easy.
Also I really recommend you the new EXP pack from AJ...new sounds and styles.
Hope it helps,
Vio