Hey, how do you install textures? Like for terrain and stuff.
Assuming you're using Windows, Windows Key + R, enter "%appdata%\.minecraft\bin\" (using the downloadable client, it goes somewhere else from web-based one) and open the minecraft.jar there with WinRAR - replace appropriate files in there.
I just did this, actually. I installed Taehl's texturepack with a modified icons file, still messing with that to make it display better.