for the cars, did you change the names of them in any way or just left it as they were, i believe that you should not change the names of the text files, or the gp4 files? don´t exactly know which of them... and did you place them in the right folders? and for the helmets the same (in case of the folders), and remember that you have to wright the names as one, MichaelSchumacher instead of Michael Schumacher, and take a look into the default.ini in the helmet folder, there must be all named correctly, too...
Dir21 =%helmetres%\%driver21%,%helmetres%\%driver21%\(%driver21%%tracknum%),%helmetres%\%driver21%\%trackname%
Dir22 =%helmetres%\%driver22%,%helmetres%\%driver22%\(%driver22%%tracknum%),%helmetres%\%driver22%\%trackname%
this ones... there must be the names that you used for your helmets instead of driver 21 and 22...