This has most likely been answered somewhere but I couldn't find it. I followed one of those perfect guides to setup, yet with a few alterations, namely didn't install Bind, so therefore couldn't install ISP Config. I went on to set up a fairly simple site, but with a couple of things like SMF forum installed. I have since installed Bind, because I wanted to install ISPConfig, yet it urges you not to install it on an exisiting setup, yet hints that they mean hundreds of sites. By installing it for one site, hosted at home, with a dyndns.org domain, will I kill my configuration at all? Thanks. (Running Debian Etch, with the usual things.) Also, you may ask why I'd bother for just one site or whatever. Well, this is all just for a learning experience.
If you are running just one site, there will be not much problems. But you will have to recreate this website in ISPConfig and the copy the html / php files from your existing website to the new website directory that ISPConfig created for you.