Ideally, you'll need a decent application for recording with.
Something like Cubase is best but there's stuff on the lower end of things that are aimed more at beginners.
You'll need a mixer so you can plug all your different instruments into it.
MIDI cables and guitar cables so you can hook everything up.
You might also need a USB interface to hook the midi up to the computer.


And that's about it. Then you just need to spend several months reading manuals and learning how to use the stuff :)