For anyone who missed the updates in the other thread http://www.atari-forum.com/viewtopic.php?f=16&t=20692
, the source code (and binaries) for the PCS generator (v5) is now available on my site for download... http://www.leonik.net/dml/sec_pcs.py
(The stuff concerning the file format is all in one sourcefile and there are functions there to compress/decompress the data).
The source can be built for a PC using GCC with Cygwin (the Posix environment for Windows) found here: http://www.cygwin.com/
..or for Atari using Vincent's MiNT cross-compiler here: http://vincent.riviere.free.fr/soft/m68k-atari-mint/
It should also be possible to build it natively on an Atari if you have the compiler setup with MiNT but I haven't tried it.
The asm source for V3 will also go on the site soon. I still can't find the source for V4 but anyone with the time could disassemble it and diff them!