How do I setup multiple sites with one database in Drupal 7

Question

My hosting provider limits the number of databases. I would like to setup several small sites with their own theme, modules, etc. The scripting for setting up drupal sites from my host provider uses simplescripts.com but when I go to do an install, only Drupal 5 has the table prefix option. Drupal 6 and 7 installs do not allow the table prefix.

I found this good reference, but it wasn't explicit as to whether or not the Drupal version mattered. How do I get Drupal to use table prefixes so I can install multiple drupal installations in the same database schema?

I guess I don't see how to add the table prefixes to a particular install after the simplescripts.com has made the initial installation.

Is it even possible to setup multiple sites in Drupal 7 using one database? If so, is it a matter of using the simplescripts.com to install the files and then moving the installed files to the location I need them to be in? or must I install Drupal 7 manually for each site?