TO ADD OR NOT TO ADD "DE" IN A SURNAME?

["Yolanda Medina-Perez" <windrocklili@...>]

HOW DO RANCHOS MEMBERS HANDLE THIS, IT HAS BECOME A CONFUSING DILEMA 
FOR ME. I PUT IN ROBALCAVA AND FOR HIS DAUGHTER I FIND HER AS DE 
ROBALCAVA....I LATER CAN'T FIND HER UNTIL I REMEMBER TO LOOK 
UNDER "DE".   I NEED SOME GUIDANCE FROM YOU EXPERIENCED GENEALOGISTS.
MIXED-UP IN EL PASO      YOLANDA MEDINA PEREZ