Multiple WordPress Installations With On Database

I have a domain where I want create multiple Wordpress installations. I want one installation per subdirectory (potentially up to 100 subdirectories). Each installation will be slightly different from the others. I can only use one MySQL database. I understand there is a way to do this by editing certain of the files in the installation. I have already created one. I need to be able to create the others. What I need is a step by step tutorial on to go about doing this. I am not a Wordpress expert so give me lots of details. If you need any files from me, just ask.