sql query help

hello all,

i have this table:

CREATE TABLE [dbo].[Table1] (
[person_id] [int] NULL ,
[dob] [varchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL
) ON [PRIMARY]
GO

with these values:

insert into Table1 values ('1', '15/12/1975')
insert into Table1 values ('1', '01/01/1980')
insert into Table1 values ('2', '15/12/1975')
insert into Table1 values ('1', '15/12/1975')

i am trying to construct a query which will return those person's with
more than 1 date of birth
e.g.
person 1 has 2 dates of birth - 01/01/1980 and 15/12/1975

thanks in advance

.