i used wp 2.7 built-in 'install a plug-in' page to install wp-dtree.
it did not upload plus.gif into /plugins/wp-dtree-30/dtree-img/
it also did not upload all gifs after plus.gif.
i would assume other files may have been skipped as well.
this problem occurred with 'install from url' and 'install from a file'
when i manually uploaded the plugin, no files were missed.
therefor, WP's 'install a plugin page' is DEFECTIVE.
unless i'm mistaken.