There are two parts in the distribution: the first one contains all the data needed to perform the computations (Weber polynomials, etc.) and the second depends on the architecture you want ECPP to run on. Each tar file was compressed using gzip.
Once you have ftp-ed all the files, use gzip -d to uncompress them. This will create the directory Ecpp among others. Go into that directory and read the file README.ecpp to learn how to finish the installation.