This page can be used to test whether or not your server supports the $_SERVER['PATH_INFO'] variable, which is required to change your URLs from something like this:
http://www.example.com/store.php?crn=1
to:
http://www.example.com/store.php/categories/books
If your server does not support this variable, Squirrelcart will attempt to set it using information stored in other variables.