ORA-01555: snapshot too old during export EXP-00000: Export terminated unsuccessfully

Seems the other sessions are updating the database during your export.
So use CONSISTENT=N ( which is default).
Dont specify CONSISTENT=Y.
Else
Increase your RBS(in 8i) and look into undo Management in 9i.
There is a long running transaction that needs more undo space than the available one.

sql >show parameter undo


NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
undo_management string AUTO
undo_retention integer 0
undo_suppress_errors boolean FALSE
undo_tablespace string UNDOTBS1



If the UNDO_RETENTION initialization parameter is not specified, the default value is 900 seconds.( I must have tweaked mine. Ingore it).

to reset this would be the command.
ALTER SYSTEM SET UNDO_RETENTION = 30000;

quoting docs

Committed undo information normally is lost when its undo space is overwritten by a newer transaction. But for consistent read purposes, long running queries might require old undo information for undoing changes and producing older images of data blocks. The initialization parameter, UNDO_RETENTION, provides a means of explicitly specifying the amount of undo information to retain. With a proper setting, long running queries can complete without risk of receiving the "snapshot too old" error.