How do you know if you're ready for kids?

I've been with my man for 6, almost 7, years now. We are high school sweethearts. We have our own home. I've graduated college. We both have pretty great full time jobs and I run my own computer business on the side. But I still feel as though something is missing. All of my friends are having kids and getting married and the "baby fever" is starting to rub off on me, or at least making me think about it. But how do you know if you're truly ready for that step?