That method which is given on digit's homepage works because of loadlin utility... if its not there then no use of extracting the ISO .... you can better burn it off on a CD... and besides most of the distros dont bundle loadlin i think... so that method is highly dependent on the availability of (1) loadlin , (2) Boot Kernel Image... (3) Native mode DOS .... like in Windows 98, and not XP
Hence , you cannot use that method to start FreeBSD installer....
Moral of the Day : Burn Linux ISOs on CD and then only install from it...