To compile the CVS version, you first have to download it! This is described in detail on the CVS Usage page. You may need to update your autoconf / automake tools as well, depending on which system you use, this in turn is described on the Development Tools page. If you have the code checked out the first step is to run autoconf and automake, to generate Makefile.in files from the provided Makefile.am files, this is all conveniently done using the bootstrap script. From the gmx directory type:

./bootstrap

If you get a message like: tar/ustar not found you will have to update your automake and autoconf tools and redo the bootstrap. Then, the next step is to run the configure script, and since this is a development version, you probably do not want to have it installed on top of the normal installation, so you can use a prefix, and subsequently build the package.

./configure --prefix=$HOME/gromacs-dev

make

make install

 You can obviously use all the normal options to configure, like --enable-mpi and so on. If this all works out then you can start using it by sourcing the new GMXRC file:

source $HOME/gromacs-dev/bin/GMXRC

(or equivalent for bash users).