The UCSC Silicon Valley Center is located in Building 19, on the NASA Moffett Field campus. (see map).
From Highway 101, take the exit Moffett Boulevard, towards the Bay (North). (If you use Middlefield Rd or Central Expressway, do the same.) Moffett Boulevard leads straight into a checkpoint, which used to be the main access control point for the NASA center. Now the security fence has been moved back; the guard will only ask you for your driver license (or other identification document, such as passport). The guard will also ask you where you are going; say "Building 19"", or "UCSC Silicon Valley Center, Building 19".
Building 19 is one of the buildings on the main quad of the campus (outside of the security fence). You can park in the rear, enter from one of the doors close to the main part of the building. My office is number 2084, on the second floor.
If you get lost, call me at (831) 459-4982.