DATETIME AS PrimaryKey?

DATETIME AS PrimaryKey?
Hi Dears!
declare @dtpk smalldatetime
select @dtpk=getdate()
print @dtpk

in the above, i m using @dtpk as a primary key value in a
table to keep a track of some events that are occuring with
a difference of one second. the above method gives me value
to store in the Primary key Filed (EventTime smalldatetime)
in the form "Dec 1 2005 7:57PM" where my requirement is
to save it in the form "Dec 1 2005 7:57:12.03PM" so as to
make it unique for the primary key field(EventTime
smalldatetime). how to get required datetime format with
the help of above statements to store as primary key in
EventTime field of type smalldatetime.

THNX IN ADAVNCE