Hello, I would like to know if someone can help me to do a bookshop for unpack a few files of textures or at least, that it(he,she) throws a bit of light and indicates me like to begin.
Pardon for the translations of goolge, they are pernicious...

Every GTAIV resource (xtd-textures for example) has got following stucture:
4 bytes - Magic ('RSC')
4 bytes - Type (version - textures has "7")
4 bytes - Flags
<<Data in ZLIB on PC and LZX on XBox360>>
From 'flags' value can be calculated sizes of SysSegment and GpuSegment of unpacked data.
Delphi:
Code:
CpuSegSiz := (flags and $7FF) shl (((flags shr 11) and $F) + 8);
  GpuSegSiz := ((flags shr 15) and $7FF) shl (((flags shr 26) and $F) +  8);
C#:
Code:
uint systemSegSize = (flags & 0x7FF) << (((flags >> 11)  & 0xF) + 8);
uint gpuSegSize = ((flags >> 15) & 0x7FF)  << (((flags >> 26) & 0xF) + 8);
Of course on PC everything is very easy because of primitive compression, but I dont know how to work with X360 data. Here it is archive which includes three examples of texture RSC.

I believe that the compression is LZX's variation.
Thanks