There is a decompression program specifically made for the PSG games; Orakio Rob's team made it and it the main tool I have used. He has it on his site
http://gazetadealgol.com.br . Go to the Diversos tab, and then Downloads. The program will be in .c format as "descompressor." You will then need to download a free c compiler. The instructions are in Portugeuse. I translated that into English for my own purposes, but Orakio Rob has not given me the okay to distribute it yet, so you
may have to ask him. However, the Portugeuse program is easy enough to use : type descompressor <FILE.DAT> [offset of the part of the file you want to decompress that starts with CM, i.e., 14000] [SAVEDECOMPRESSIONFILENAME.DAT]>[SAVE
PRINTOUTNAME.TXT]
You can do alot with the printout, though placing it back into the file so it can be in the game without breaking it is a little more complex. You cannot place the the decompressed section completely: you have to splice it in,change flags in the CM
header, and then at the beginning of the file. When I am done with the PSG1 translation, I plan on making a small tutorial about how to do it.
In the meantime, I hope this helps you get acquainted with the tools,so you can play around with it
What I have had to do was use UltraISO. Do a Google search for it. If you have a PS2 ISO already, simply open it in UltraISO.It will show the files that are within the ISO.Simply extract these files. The ones you would be editing text-wise would be the SLPM file and the EVENT.DAT file. I edit these in the MadEdit hex editor - it is also free and allows you to see the hexcode as SHIFT-JIS, which is what the Japanese is written in. There is a limited amount of English letters already encoded in the game; Using MadEdit,open the SLPM file and scroll around until you see a long list of letters;
it is usually in the first 50% of the file. When you edit the file, save it, and place it back into the ISO using UltraIso. Before
you save, you MUST go into the options and make sure "change checksum" is OFF. Thus, the original game's checksum is preserved. Then, simply load the ISO as you normally would into the PCSX2 emulator and play