packing-format

you might try to post something here:

http://groups.google.com/groups?hl=en&lr=&group=comp.compression

[ArC]

this file has no crypto or something else, all files are in plain there...

Well if all files are in plaintext (as I understand from this statement) then it
should be easy to write an own unpacker for this un-gz-ed file.
What you have described looks like a structure of the following format

struct ungzfile
{
unsigned long dwOffset; // Offset of the file
char szFilename[256];    // name of the file, maybe more than 256 bytes
}

So if you wanted to extract all files you just "read out" this structure and store all offsets in an array until you reach the offset of the first entry. Now that you know the offsets of the files you can extract them.