In San Andreas, models files have the extension, .dff(Render Ware binary stream file).
They are hierarchically structured binary data files used by the Render Ware 3.x graphics engine utilized by Rockstar North (on PC, PS2 and XBox,)
Texture files have the extension, .txd; for links for tools for modifying textures see below. .dff files can be opened and edited with tools, such as, 3d's Max, G Max, and more.
RW streams are split up into sections. Each section has a 12 byte header and can either be empty, contain data or more child sections. Section content, especially of data sections, is determined by an ID in the header.
There is only one data structure common to all RW streams - the section header:
4 byte - DWORD - section identifier
4 byte - DWORD - section size, including child sections and/or data
4 byte - DWORD - RW version ID
The RW version ID varies depending on the RW engine version used for exporting the files. It must be the same for all headers within one file. Backwards compatibility is very limited.
Auto Desk 3d's Max
3DS Max/G Max import/export
2dfx export from 3DSMax
List of RW section ID's