Hello gildor,
thank you very much for your interest... I feel like a kid with a new toy

here is all the information I could gather on the Internet, plus my experience in my time working on this.
Where I can find specification for that texture format
Information:
G16 – 16-bit Grayscale
Primarily used for terrain heightmaps, G16 textures offer 65536 levels of gray, providing greatly increased precision of grayscale information for those rare cases where it is needed. Most external graphics applications are not able to handle 16-bit grayscale information, however, so manipulating G16 images outside of UnrealEd may require specialized software, such as G16ed. RGBA8 and P8 textures can be converted to G16 in UnrealEd by setting the texture as a heightmap for a terrain, and once it's visible in the Terrain Mode window, right-clicking on its thumbnail and selecting "convert to G16" from the pop-up menu. (Import/export formats: BMP Note: The G16 "BMP" format is not actually a valid BMP file, and will not work correctly with most programs)
More info here:
http://wiki.beyondunreal.com/Legacy:Texture_Format and here
http://udn.epicgames.com/Three/TerrainAlphamaps.htmlSample code:
On this site
(UEdTexKit) you can find a set of tools (source coded included) that lets you convert TIFF images in G16. also this apps can do this:
G16edHMCSwhat application I can use to test extracted texture
I use the software
UnrealEngine2Runtimeto draw and edit this images, but first the Lineage file must be decrypted so it can be read by the application, to open it go to C:\UnrealEngine2Runtime\System\UnrealEd.exe
I also use this software
(Unreal Tournament Package Tool) to view and extract images of such files, the problem is that the image are not exported in G16 format, which trigger a loss of image quality

Sample OLD UTX Lineage decrypted file, You can open this file with the above program:
http://www.4shared.com/file/ZD3VNzkt/decrypted.htmlSample NEW UTX Lineage encrypted file. You can't open this file with the above program, but you can extract the images using "umodel" (except the G16 BMP):
http://www.4shared.com/file/3MNqgLYk/new_file_encripted.htmlExample of an image in G16 format, extracted from OLD UTX Lineage decrypted file:
http://www.4shared.com/file/ko-K2L3w/G16_IMG.htmlOn the desktop or browser this image is displayed in color, but if it is imported in its native program (Unreal Engine) or HMCS is a gray scale

Best regard,
Cuba