Don't think there are high res texture packs as such for the game - due to the problem with pure server and anti-cheat - depending on how the LAN is setup you may get booted from the server and/or the texture pack won't load while connected to that server.
Most people who play the game online go for the settings that give the clearest view over high quality visuals, often using mostly very low settings, so its not something thats been a priority for the game.