These two utilities were referenced in Dan McCabe and John Brother's article, titled "DirectX 6 Texture Map Compression", which appeared in the August 1998 issue of Game Developer.  These two utilities compress textures into the S3TC format.  S3TC.8BI is an Adobe Photoshop plug-in that compresses images into the correct format for use with the S3TC texture compression standard.  The other utility, S3TC.EXE, is a stand-alone compressor that does the same thing. 