I beleive, with 8i you cannot store Milliseconds in date column. you need to have a varchar2 column. And the standard workaround is to use a JavaStoredProcedure.
anyhow with 9i it is just native.
SQL> ed
Wrote file afiedt.buf
1* create table tstamp ( t timestamp(1))
SQL> /
Table created.
SQL> ed
Wrote file afiedt.buf
1* insert into tstamp values (TIMESTAMP'2002-06-14 15:50:30.1')
SQL> /
1 row created.
SQL> select * from tstamp;
T
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14-JUN-02 03.50.30.1 PM