How far North do I need to drive from Hearst Castle before I get into the beautiful coast-line drive commonly referred to as "driving Big Sur"? I won't have time to drive all the way up to Monterrey,but I wanted to get in part of the Big Sur experience.

I think it will take you no more than two hours. When you get to Big Sur, splurge and stay at the Ventana Inn, one of the most romantic places on earth. To get in the mood, rent the old movie The Sandpiper with Elizabeth Taylor and Richard Burton. There is nice hiking up the hills to an amazing 360 view of the coast, hills, etc. The beaches are lovely tho breezy. Your personal outdoor hottub under the stars and your perfect fireplace and your goosedown comforter back at the Ventana Inn will warm you up afterwards!

I'd say it takes about 2 hours.

Just north of Hearst Castle is a place called Ragged Point and that is the beginning of what people call Big Sur. There is actually a town of Big Sur but that doesn't matter and you don't have to go that far. Most beautiful park IMHO is Julia Pheiffer State Park and you can probably be there within an hour from Hearst Castle if you don't get dazed by the views and stop every 10 minutes like most folks do. To drive the whole of hwy 1 through "Big Sur" is only 90 miles but can easily take 2-3 hours. The drive in most people's minds ends in Carmel, not Monterey. Be advised though, that if you don't drive the whole way, there is no way to cross the mountains to the freeway. You'll need to turn around somewhere and come back south. Ventana Inn mentioned above is luxurious and a fantastic place---of course, you'll pay to stay.

You should also stop at Nepenthe which is a nice shop and restaurant. The view is spectacular. It is right on hwy 1 in big sur.