newbie help

Hi All, I would like to setup a system something like this

                                                                               customer A
                                                                                /        \
                                                                                  cust 1        cust 2
                                                                                 /      \              \
                                                                    cust B       cust C          cust D

customer A has customer 1 and 2, cust 1 has cust B and C etc, etc. what i'm after is when a customer user logs in he can only see record of its customer, e.g cust A logs in, it can only see records of cust 1 and cust 2, if cust 2 is login it can only see cust D and so on how would i approach this? should every customer have it's own database, consisting of all tables i need e.g customer detail table, and i will use the database name as session variable, so that when they add records it be inserted on table under that database? sorry if my questions are confusing, hope anyone can help me, i just need help on how to approach it at the beginning so it will not be messy later on. Thank you. Regards, Nhadie