Alt Link Text can be used to modify the link text and title attributes of links in page lists, and to remove pages from page lists completely.
Alt-Link-Text uses the add_meta_box() function to create new fields on the Write Page and Manage Page screens. This function was introduced in WordPress 2.5.
No. At the moment, Alt-Link-Text is not WPMU compatible.
No. If you want to remove all trace of the plugin from your database, then you need to uncomment lines 56-58 of your alt-link-text.php file and then deactivate the plugin.