How do I calculate drainage density with ArcGIS 9.0?

I have the hydro toolbar installed and have stream networks etc. I need to calculate the drainage density but have not found any tools to do this included in the programme. Maybe I'm missing something? I've also checked the rest of the internet for online lectures from other universities and have not found them to be of any use to me. If anyone knows how to calculate d.d. or can refer me to a site with step by step instructions then I'd be happy because I've been trying to figure it out for about a month now!