Up until a few years ago, making music meant a massive investment in time and money. Those days are fortunately gone now, you can use your computer to record and edit your instruments or vocals, and burn a CD of your work
In order to make music with your computer, the minimum you need is a soundcard and good software. Some soundcards come bundled with a microphone already, those are usually of poor quality and not suitable for decent music production.
You might also want to look at the applications that are given away for free on cover CDs of music magazines or those that come bundled with your soundcard. Some music software developers give away older, discontinued or feature-limited versions of their software for free.