||You are, therefore, based on your comment, "Under DOS in a PC", probably running PC-ArcINFO. I am not sure if you need to have purchased extension for PC-ArcINFO in order to execute more sophisticated routines.
You need to look into the documentation of the version of Pc-ArcINFO you have and see if there is a command similar to IMAGEGRID available. Search the help files for PC-ArcINFO so see if there are references to manipulating images, and to see if you can then access your command.
For ArcINFO, GRID is a program additional to ArcINFO, that one needs to purchase. I believe it is the same for PC-ArcINFO, and, therefore, without the purchased extension of GRID, the command does not exist, as it is not possible to perform the routine without GRID available.
I have not worked with the file format you are identifying, but your first step is to do a little research into how complete your version of PC-ArcINFO actually is.