What's the best way to get around Sunnyvale, CA if you don't have a car?

I will be going to Sunnyvale, CA for a few days for a business trip, but I'd like to be able to go to Palo Alto to visit the campus and maybe head into San Fran for a few hours. What is the best way to get around Sunnyvale or the area? I've noticed people talk about taking a train around. Can you provide details about the train system (price? reliable? is there a better way?)