Thats right...you can't edit it unless he gave you the .z80 file as well. it is written in assembly. there is another way to execute it i believe. if you have the plus then you *should* be able to execute the program by pressin [2nd]Catalog then finding Asm( paste that on the screen. then find the program in the program list and paste that in the screen. you should also be able to execute it that way. not completely sure. assembly is extremely difficult compared to languages like c/c++ i am trying to learn a little but it is pretty complicated as there are no variables....just raw memory adresses that have to be in hex. and all of the commands are different also.