Cascaded Inserts And Updates?

Hi

I have 3 table (tbl1, tbl2, tbl3).

tbl1 colums ---Pid(autonNumber),Pcode(unique values),PGuid

tbl2 columns---Pid, CatId,Fid

tbl3 Colums----Pid,BundleId

Using Trigger(After Insert) in tbl1 to insert the data of tbl1.Pid to tbl2.Pid and tbl3.Pid . tbl1 will be uploaded with new rows and existing rows will be updated from the csv file.

Trigger in tbl1 works fine by inserting data to tbl2.Pid and tbl3.Pid.

My questions are :
1. Is it possible to use trigger to update tbl2 and tbl3 if records exist if not insert new record to colum Pid in tbl2 and tbl3 from Pid of tbl1

2.Or is it possible to use sql procedure to do cascaded updates or inserts by merging datasets from tables and csv file using asp.net

3.Or How can I use single Trigger to insert if not exist and update if data exist.

4.Or Do I have to use two trigger one for insert and one for update. If this is the case how do check for data existance.

After insert Triger I am using at the moment is below (replied as an answer in this forum for my previous thread)

create trigger t1 on tbl1
after insert
as
begin
declare @id int
select @id=pid from inserted
insert into tbl2(pid) values(@id)
insert into tbl3(pid) values(@id)
end