There is a much simpler answer; go into the bios and disable the install mode.
Windows NT 4.0 wouldn't install if the system had 512MB or more. So manufacturers offered an "install mode" in the bios that just capped the usable memory to 256MB so you could install NT. Once the OS was installed, you'd go back into the bios, disable install mode, and have access to all memory.
Member since 2003