Hi Sophie, good news is that you can get realy good software for free - download Reaper here: http://www.cockos.com/reaper/download.php

All you need to get is a soundcard with at least one 1/4" jack to allow you to connect a microphone and/or guitar lead (an XLR connection would be handy too - that will allow you to hook up a proper microphone like an Sure SM58). Check out M-Audio stuff for good quality at reasonable prices - just make sure that the soundcard has a preamp in it that allows you to go direct to your sequencer (so you don't have to go and buy a separate preamp).

A midi keyboard will work with Reaper, all you need is a keyboard that can connect to your pc via USB.

Hope that helps, if you get stuck post back.