How to start trace of an existing session in 10g

10g has a new package called DBMS_MONITOR

EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(&sid,&serial,waits=>true, binds=>false);

To disable

EXECUTE DBMS_MONITOR.SESSION_TRACE_DISABLE(&sid,&serial)

My old article on tracing

http://oracleappstechnology.blogspot.com/2007/07/activate-extended-sql-trace-for-given.html