Disclaimer: I'm not responsible for any damage that could happen to your devices following this guide. It' under your own responsability!
Here a brief description of the steps needed to deploy a W8 WIM image to a BIOS computer:
1. put the WIM image on some sort of USB device (i.e. install.wim)
2. boot the computer with some sort of bootable media that contain DISM (i.e. AIK cd or the W8 installation dvd or AOEMI Backupper or anything else)
3. once booted, from the prompt enter:
select disk 0
clean <--- be careful! this will erase the content of the disk!!
create partition primary size=350
format quick fs=ntfs label=System
create partition primary
format quick fs=ntfs label=Windows
Let's say install.wim in in the H: drive in a "win8" folder:
dism /apply-image /imagefile:h\win8\install.wim /index:1 /applydir:w:\
now you have the windows file in the W: disk, we need to make it bootable
bcdboot w:\windows /l it-it /s s: /ALL
reboot the pc it should load now the Windows 8 OS just installed