Hey Gibbersome, Welcome to the boards!
Just a heads up, since you are new, it's often hard to take anything said here on face value. You really have to know who's saying it to know how valid it is.
Take everything with a grain of salt!!!
On hybrids in general - remember that just because two species can not produce fertile offspring doesn't mean they can't produce any offspring. Mules and Ligers are good examples of sterile hybrids.
On Human/Gorilla or Human/Chimp hybrids - don't think it's possible. HAven't seen any evidence for it.
You may want to look up "Humanzee" on Google to get a link to Oliver - a bonobo (a species of erect walking chimps that doesn't get enough press) which was often billed as a human/chimp hybrid. He wasn't.
As for Bigfoot's origins - I'd look into information about gigantopithecus, an extinct (?) species of ape from Eastern Asia. Seems like a better culprit than a hybrid.