All these files are compressed with the "gzip" program. To uncompress them in Windows, use winzip or a Windows version of g[un]zip. Also, please don't just download these for the hell of it -- they account for 95%+ of my HTTP traffic bytes.

cegtges.bin.gz	created from the CEGT 2005 games -- a good "small" book
twic.bin	created from "The Week In Chess" magazine PGN files.
large.bin.gz	the opening book that typhoon uses on ICC