This tutorial is no longer of use. Both XCC and FinalBig can now open and save the B4ME BIG files. Do NOT try this for fun, as you dont need it.
Download XVI32 from
this page.
Open INI.big with it.
You'll see two windows, on the left something unintelligable, the HEX, on the right normal characters. The first four letters are BIG
4. Change the 4 into a F so it reads BIG
F
Now XCC Mixer and finalbig can read it.
I dont think I can make it easier.