I have attached a PDF that explains the use of a custom splash screen.
The PDF links to another Intel page that is also down, but it has been archived:
https://web.archive.org/web/20090224102258/http://intel.com/design/motherbd/gen_indx.htmThe utilities listed are not available on the Internet archive but I did find them with a cursory Google search...
They do confirm that it is the Intel flash utility that is used to load the image, but of course you don't have it...
Well maybe you could capture it with a capture card

If you just want to disable the Gateway splash screen you can do that by enabling "Silent boot" under the "Boot" menu in the BIOS.
P.S: Here is the help output taken with a HEX editor from iFlash.exe, of note is the "user area" that I guess would be saved with the option: /sU
GUI-mode options:.
/m - Monochrome display
/b - Use BIOS video calls.
/t - Use EGA/VGA line count
/n - Do not use pointer device.
Command-line mode options:.
/h - Help (this text).
/q - Quiet mode; errors only, and no prompts.
/qb - Quiet mode; No beeps. Standard options:.
/r - Force reboot after update
/@ - Use override file.
/f - Force CMOS defaults next POST
/d - Verbose debugging output.
/p pathname - Program FLASH device with contents of 'pathname'..
/nr - No reboot when complete (SMI flash method).
/rb - Reboot before update (non-SMI flash method).
Special Operations:.
/v pathname - Verify current flash with contents of 'pathname.'.
/x pathname - eXamine flash header of 'pathname'..
/sX pathname - Save resident flash area to 'pathname' (or 'vvvv'BIOS). X = { 'B'IOS, 'L'anguage, 'U'ser, 'R'ecovery } area..
/ae - Erase OEM CMOS Defaults..
/ac - Copy Custom CMOS Defaults into the OEM CMOS Defaults..
/af - Force OEM CMOS Defaults next POST..
/ag pathname - Get OEM CMOS Defaults to 'pathname'..
/as pathname - Set OEM CMOS Defaults with contents of 'pathname'..
/ew pathname - Write BMI settings with contents of 'pathname'..
/er pathname - Retrieve BMI settings to 'pathname'..
/md - Load default modules only (like recovery)