Hi
It would help to know what are your Oracle & SAP version.
What is the whole DB size ?
Which tables are getting that big (you cannot setup partitioning on all tables). Check note 706478 - Preventing Basis tables from increasing considerably).
Did you experience performance problem at DB level, globally & for these tables ?
Did you ever reorganize these tables ?
Compression could help (especially OLTP compression on 11g) to reduce the table &/or index size.
An other solution to you problem could be to perform some archiving operation, maybe with the help of the partition engine.
Regards