Thx xenon2k,
I'm gonna go back an edit my original image and see how it goes I think - I must have messed up my current image I think.
btw, a good Hex Editor for doing large files (larger than the amount of physical RAM you have) I've found is Hex Edit 2.5 by Expert Com Soft if anybody else wants a quick editor than can do huge files. Shame about the trial limit tho!

hoho
Many thanks guys everybody for helping out!!