you'll need some kind of software to arrange some of those things into tunes...(Cubase is the standard because of the VST effects)

You might want to have a mixer too, to bring down the volume of the 505 to a reasonable level (If you put it straight, you might hear digital distortion, the worst kind ever).

If you plan on doing a lot of tunes, you'll need a big hard disk (20 giga is a minimum nowadays) who has to be quite fast too (usually 7200 TPM)

Of course, connect your 'line out' to a good stereo system, because most computer sound systems suck.

Enjoyyyy...