You need:
gzip compression utility, or alternatively bzip2
that you find on
ftp://sunsite.unc.edu:/pub/Linux/utils/compress;
this tool compresses better than gzip, but it's also a wee bit slower
and consumes a lot of memory;
upx executable compressor, whose home page is at
http://cdata.tvnet.hu/~ml/upx.html and
http://wildsau.idv.uni-linz.ac.at/mfx/upx.html;
zlibc package, available on
ftp://sunsite.unc.edu:/pub/Linux/libs/compression. It's
called zlibc-X.X.tar.gz, where X.X is the latest version.
There are other executable compressors. One is gzexe (forget it), while
tcx was probably the best before upx became available; yet another
is tzx, in theory better than tcx. The thing is, it screwed
everything up when I tried it on a spare PC, though I'm not sure if I did
something wrong. You had better stick with upx: it's reliable,
efficient, and very handy.
There are kernel patches that provide transparent file system compression a la Stacker, but as of this writing none of them has yet a reputation for stability and reliability. For safety's sake, steer clear.