ok now you need to use BWViceBuilder13...u can download it at here
u can use the codecreator in side it where you can found in this tool...open it and then open your GTA Vice City and play the game...the codecreator would read the coordinates for you, the codes are at the bottom right
copy it py pressing Ctrl + C and press Ctrl + V to paste it at the decompiled MAIN.SCM where you want the vehicle, items, weapons or checkpoints to be created...there are lots of coded text documents in the zip
u need to remember to decompile your MAIN.SCM and backups!