We're going on vacation, and we plan on taking my brother his computer. Will a computer survive in a hot car for 4 days? Would putting it in a cardboard box help?

Hi
PCs, and especially Hard Drives are sensitive to vibrations.
If you have to do it, turn it on its side, so as to minimize the chance the heads touch the platters. Avoiding country roads will help too...

As for heat, I wouldn't lose any sleep over that-its not my system anyway- so far as you keep moisture to a minimum.

Thanks! I'll be sure to put it on it's side.