"Gp3Video.exe is a small DOS program that will patch your un-encrypted Gp3.exe
file. As a guideline, this file must be at least 8,822,784 bytes long,
preferably of exactly that size. If your un-encrypted Gp3.exe is of a different
size I would question its integrity.
Since Gp3Video.exe will patch your Gp3.exe, make sure you save a copy of it
before proceeding. Then simply run Gp3Video from the Gp3 directory. From now
on I will refer to the modified Gp3.exe as Gp3Video."
If I read it right, it only works with the original GP3.exe, why don´t you use fraps ?
Happy racing from Germany !!!