admin – settings – miscellaneous
this defines your uploads folder
There is this plugin http://wordpress.org/extend/plugins/add-from-server/
Use FTP to upload into the folder mentioned by samboll, then use the plugin to import into the Media Libarary.
Is it possible for the media library folder to look at other folders at the same time? It would be nice to be able to upload images via other plugins and have them appear in the media library. I tried the above plugin and it works great. It would be nice though, if I didn’t have to copy (duplicate) images and use more serverspace than needed, and also not having to manually update the folders via Add From Server ever so often.