Try dpkg --help; the option names such as --no-also-select that are mentioned in the installation manual are out of date (last time I looked at the install manual).
Installing from dselect is all you need to worry about; you don't need to drop down to using dpkg. I don't know what's up with gzip. You must first determine whether it's your gzip or the .deb files or something else that is the problem.
