Hello Lamaringtasa .
I am here to help you . OK here goes the solution :
you must open the requested files with notepad for instance right click on the Data\Vehicle.ide and then select
"open with" then select "notepad" then a notepad file will be opened .
then replace the stuffs.
but for opening Models\gta3.img you must download the Image Tool from this site because that file is too
big for notepad .
Bye
Vinewood Boy