T here really is no fixed answer to your question, its all about preference. Questions to ask yourself are what do you expect to acheive from your set up? Do you intend to make instrumentals or full vocal tracks? What genre of music are you trying to make and is there an established way of making trax for this genre with a popular set of standard tools?
For example you might need a slightly different set up to make a vocal heavy R&B track as opposed to a beat heavy Drum and Bass track with lots of effects going on.
If you dont have a direction and just want to have a go at making music then a basic computer set up eg. G4 Apple mac working with a self contained studio program like Steinberg Reason, or a basic PC with a program like Fruit Loops (very basic) may be the way to introduce yourself to it all. You want to go deeper, you'll be straight with say, the G4 apple mac running a sequencing package like Logic and a small control keyboard. You'll also need some sound source to go with this like a sampler (Akai proffessional range) or a sound module like the Proteus 2000.
With todays technology, there are so many ways to do this it's ridiculous, and the best thing to do is to demo equipment with an established music equipment retailer. I would recommend the Digital Village chain where you'll be under no pressure to actually know anything at all and can ask for a demo at complete starter level and explain your intention and what you expect to achieve. With so many options available it really is about what works for you, given your finances and available space.