Multiple Installs on One Site

This would be perfectly possible either using the multisite feature of wordpress (this uses one wordpress install but allows production and admin of multiple sites from same place) or alternatively (and this is probably what you mean) is to use different table names for each site.

To do this you would setup your database and three users (for security – one for each site). Install wordpress in one directory and use a table prefix of (for example): “wp1_” and use one of your users to access this.

Then install another wordpress in another directory and use another table prefix (for example): “wp2_” and a different database user.
Then repeat for the third site and so on.

Hope that helps
Aventura

P.S. Not entirely sure whether the three different users makes it more secure as they can each access the entire database but there is a way to restrict them to certain tables in phpMyAdmin I believe.