I suggest you put in a special byte sequence at the start of the data which is lengthy and complex enough to ensure that it won't appear elsewhere by accident. Your program can then search for that, and read on from there. The next section being a header which contains data about the files, and the next being the files themselves.
The char equivilent of "HALOSINSTALLER" for example :)
The char equivilent of "HALOSINSTALLER" for example :)