can we increment the column --autimaticallyis there any possiblity with tiggers

hi,
i am a beginner to ms sql server2000
i have a table
create table ddd (a int, b int)
by table structure is a b
now when i enter a value in b column suppose '2' in column b
bext time when i insert a value in the column a i have to get the value
in b as 3 is thi spossible with triggers
insert into gdg values (1,2)
a b
1 2
insert into gdg (a) values(2)
a b
2 3--> i have to get this 3 automatically
is there any method to get this
pls help me
satishis this homework?sql