What do 'von' and 'zu' mean in German last names?

Von is 'of' so that probably means a pre-unification 'family name' like Mecklenburg etc. Is that right?

What about zu?

I thought about that when I heard the name zu Guttenberg (Karl Theodore). Looked on wikipedia but his name is von und zu Gutterberg HUH???? WHAT DOES THAT MEAN?

Short:
"Von" means that somebody's family comes from that particular place.
"Zu" means that their family are still in possession of it.
"von und zu" means both

More reading;

http://de.wikipedia.org/wiki/Adelspr...at#Deutschland