I hate to dispute the plugin author, but he's incorrect. The plugin is in fact hardcoded for configurations where WordPress is stored in the site root.
Line 128 of pluginst.php defines the variable $toggle, which is then output on line 148 as part of the Uninstall table. Here's line 128:
>$toggle = "<a href='/wp-admin/plugins.php?page=".$_GET['page']."&uninstall=".$plugin_file."'>".__('Uninstall')."</a>";
As you can see, the link will always point to your website's root. To get the plugin to work properly, change line 128 to this:
>$toggle = "<a href='" . get_bloginfo('wpurl') . "/wp-admin/plugins.php?page=".$_GET['page']."&uninstall=".$plugin_file."'>".__('Uninstall')."</a>";
get_bloginfo('wpurl') will return the location of the WP installation, as you've defined it under Options -> General in the "WordPress address (URL):" field. I'm not sure, but I believe 'wpurl' is only available in WP2.1 and higher. For older versions, you'll need to use something like get_bloginfo('siteurl').
Anyway, I made this change and was able to use this plugin to both install and uninstall other plugins under WP 2.2RC1.
Edit: fixed typo. Oops.