VPS would be like having a computer on-line with a desktop, Seed box is like an online torrent client. They usally have a webwebui witch gives you a couple options like = rutorrent, file manager, news, chat, network storage, Wiki

So VPS is like a little computer witch you can install stuff on like flash player (if you have root access) Seed box is torrent client with a webwebui interface (They usally dont have all the options your home torrent client has ports and such) but some come with a proxy service. Hope this helps