All GeForce based boards support DXTC (aka S3TC) texture compression and can decompress S3TC and DXTC textures in hardware.
DXT1 decompressor, integrated in all GeForce graphics processors, uses 16-bit texel interpolation. It can cause terrible banding effect on some textures, which contain smooth color gradients (e.g. sky textures in Quake III). The rest DXTC formats use 32-bit texel interpolation and give much better image quality in cost of some performance drop. Modern games (like Serious Sam) can allow user to select compression format. But some games, which had been published before discovering this problem, can give bad image quality on GeForce boards when texture compression is enabled.
NVIDIA had implemented S3TC quality trick in order to improve image quality in such games. S3TC quality trick works on Detonator 6.47 and higher and it can be enabled via RivaTuner's OpenGL settings. This trick forces driver to create DXT3 textures instead of DXT1. But if you are using old drivers, you can force texture compression format on application level via S3TCFixPack scripts.
This patch script can force Quake 3 to use any of 4 supported S3TC formats (it uses GL_RGB4_S3TC format by default).
