Try the microsoft tool if you are on a Windows box for a workstation. It works with any kind of site (IIS, Apache, etc). It works excellent (and is much nicer than ab). You just open your browser, surf a bit on your site, and it will record what you do (cookies and all). Then start it up and it will do the same thing you did when surfing with a configurable number of client threads, etc.
The website for it contains lots of documentation and other resources. Oh, and it is also free 🙂
http://homer.rte.microsoft.com/
Jack