The bitcoin network already has more hashing power than the worlds 100 top super computers. I haven't tried mining
It would be worthless on a normal PC you would spend more in electricity than you would get in coins
you could generate some with a high end graphics card, but most miners are now shifting to asics which are specially designed processors for this type of application
I imagine a government could take on a program to generate more PC power than bitcoin, but it would be cheaper for them to just attack the exchanges like they did with poker and banks