look in your carsets folder - normally 'C:\Program Files\Grand Prix 4\GPSAVES\Carsets\'
go to your 2005 folder and look for 'Data\Cars\Ferrari\Enzo'.
now uo should see Imola and MagnyCours folders.
if you downloaded Enzo's ferrari and extract it to 'temp' i think you should end up with some gp4 files, some tex and some more inside a 'NT' folder.
put all the files from 'temp' into the 'Imola' folder in the set, and all the files from 'temp\nt' into 'MagnyCours'
let it overwrite the current files - they are 0kb placeholders.
now you need to copy the lod_0 files and rename them lod_1
ie: car_ferrari_car1_lod_0.gp4 -> car_ferrari_car1_lod_1.gp4
that should do it.
____
Tony