`Endian'? Where did this file come from/go to? Are you sure it's big endian (most PCs use little endian, I thought only the big stuff -i.e. mainframes - use big endian)? Whats the application for this "thing" you are writing?
Past that, I will try and read up on the topic again to chime in further. "Big endian: byte order ='s floped" would be about the extent of my endian knowledge at the moment.
Generaly speaking though:
Do you have any idea what the format of the file is you are trying to read? When you get to a location you kinda have to know (or have an idea) as to what you expect there ...a letter, number, start of a string, image, credit card numbers, etc., etc..
Sorry I cant be of more help right now but I don't remember much about this topic and I only read up on interpreting data-big/little endian once so I wasn't all that keen on it to begin with. However, I will try to do some reading tonight.