How to build your own cars.wad is in the FAQ. Each car has to be downloaded separately, then given that you have a laptop with on-board graphics, you have to reduce the lods. This is not an easy job. Then you have to unpack the wad and insert the cars, then re-pack it. I respectfully suggest you wait until you get a better machine that has the capability to run the mods that are designed for better machines.
[
www.mediafire.com] Some say you should click it, you know you want to.
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www.gp4central.com] <----GP4 Central