There's no especial difference; GD1.6 does do GIFs but doesn't do truecolour images, is all. Replace [man]imagecreatetruecolor[/man] with [man]imagecreate[/man] and [man]imagecopyresampled[/man] with [man]imagecopyresized[/man], and it ought to work without much further effort.
Or consider getting a more responsive host.