You can obtain it from http://www.cpmd.org. Read and agree to the terms of the license and apply for a license. You will receive your password by e-mail.
Almost any platform with a Fortran77 compiler supporting the Cray pointer extension. It is preconfigured to run on IBM AIX, Linux, SGI Irix, SUN Solaris, HP HP-UX and Tru64 UNIX, NEC Super-UX, and Hitachi HI-UX/MPP.
You can use any Fortran compiler supporting the Cray pointer extension. The compilers from Intel, Absoft, and PGI are known to work. A good resource for CPMD on Linux is here.
Both f2c and g77 do not support the Cray pointer extension to Fortran77 and therefore cannot compile CPMD, but it can be compiled with gfortran, the new GNU fortran compiler.
After unpacking the sources, choose a reference configuration, customize the generated Makefile, and build the program. This process could e.g. look like: ./Configure ./Configure IBM-SP4 > Makefile vi Makefile make
Please, have a look in the CPMD mailing list. Most likely, your problem is already covered there. If not, you can send an e-mail to cpmd-list@cpmd.org. Please register before writing!