Thanks to recent developments in Nintendo 64 emulation a variety of texture-enhancement and replacement projects have sprung up. The most active are ones related to the two Nintendo 64 Zelda titles. These packs only work under emulation (and only under 1964 and Project64 at that) and will not work on a Nintendo 64 or GameCube.
The thumbnails do not do these graphics justice; even at 1024x768 everything is still smooth (the original game ran at 320x240, but emulators can use any resolution your monitor supports). However a much more powerful computer is required due to the vast increase in texture resolution.
Originally called Federelli's High-Res Texture Pack, this project contains contributions from many avid fans and is still under construction. The aim is to replace every single graphic element with a faithful high-resolution equivalent. Federelli has since handed over project management to KMan, and it continues to develop.
This graphics pack makes the game look as much like The Legend of Zelda: The Wind Waker as possible. Because models cannot yet be replaced all changes are limited to textures only.
This new project aims to make the game look as much like The Legend of Zelda: Twilight Princess as possible.