Compress::Zlib and IO::Filter will do compression/decompression but are not (as stefp points out) perl only modules and it looks to me like everything invloving zip or compress on cpan uses Compress::Zlib (PerlIO::gzip, MIME::Decoder::Gzip64, IO::Filter::gunzip, Archive::Zip)

here is the rfc on the gzip spec if you feel like writing a non Compress::Zlib module.
-p