Yep. Thanks to advice I've downloaded and unzipped the file to a /download directory that I created specially. And yes, when I look, lo and behold ls /download/install_ispconfig/ reveals that there is a file called setup. Excellent.
As I have never run anything like this before please, how do I actually install ISPConfig from the files I have got and what directory should I put the installation into, or does it do it 'all on its own'?