On this page:
Requires WordPress Version: 2.2 or higher
However, using it with version 2.5.1 gives the following error:
Fatal error: Call to undefined function: admin_url() in <path>/wp-content/plugins/wp-super-cache/wp-cache.php on line 1395
Some searching indicates that the admin_url() function was added in WordPress 2.6 (it seems), making that the minimum supported WordPress version.
The page should probably be changed.