You'll need GNU make and OCaml 3.08.3 (earlier versions may work, but untested). First edit 'src/make.rules' and set the appropriate platform name - just comment out PLATFORM_NAME=win32 and uncomment PLATFORM_NAME=unix. Then just make in the src directory.
There is a slight hitch, in attempting to make things easier I've left the depend files in the src tarball. Unfortunately they were made with the windows version of ocamldep and so the path separators are wrong. You need to do the following in the src directory:
make depclean
make depend
make
UPDATE: I've been told that certain versions of OCaml 3.08.3 don't support -ffast-math as an option to ocamlopt. This was reported for Gentoo building the OCaml distribution from source. If the build fails you'll have to remove that flag from all the Makefile.mk in each directory (I'm looking into completely revamping the build system).