Are you talking about a format thatworks in a similar manner to blizzard's MPQ ?
That works in the manner u describe, you compress all your files into one large file, but they essentially becomes "blocks" in the file rather than individual files with names/paths etc...
If this is the case, depending on the type of asset it is, would determine how you would load it. For instance, if it was an image, you could load the "block" that contained the image data, create a blank GDK image, and just copy the pixel info over... that would work in a similar way for meshes, although memblocks are a GDK think, so I dont know that it would work...
If it ain't broke.... DONT FIX IT !!!