Well, if you can fly into San Jose Int'l Airport, that would be much easier. But assuming you are coming from Europe, then I understand you have no choice.
From SFO, the public transit options are not too difficult. From the International Terminal, board the BART train (http://www.bart.gov). Ride one stop to San Bruno, get off, then catch the Millbrae BART train. Ride one stop to Millbrae, get off, and then catch Caltrain (http://www.caltrain.com).
This is where I/we need more information. Which hotel will you be staying at? There are three different options depending on where in Santa Clara you will be staying. They are:
1. Get off at the Lawrence station.
2. Get off at the Santa Clara station.
3. Get off at the Mountain View station and transfer to the VTA light rail (http://www.vta.org/schedules/SC_902.html).
Note that not every Caltrain train stops at every stop, so check the schedule before hopping on board. Also, despite the multiple transfers, this will not be any more time consuming than taking the Monterey Airbus to San Jose Int'l Airport then transferring to a shuttle or taxi.