How is a PRNG used in the PGP? I'm currently reading up on the components of PGP and I am wondering what exactly the PRNG is used for. PGP uses ANSI X9.17 and entropy from a users keystrokes to generate a temporary key.

So, is this temporary key used for the public key encryption? Is it one of the keys in the key pairs? And how does PGP actually generate it's key pairs?
(Open)PGP is a hybrid encryption system, it uses both public/private and symmetric key encryption. Public/private key encryption is very inefficient for any kind of data but very small one, so when encrypting for some private key, usually you're only encrypting some block cipher which is then used to actually encrypt the data.

For generating this key, a random number generator is used.