I am seeing a train from Wien Meidling to Warszawa Centralna leaving at 22:23 on 19.05.11 for 75EU (2nd Class) and 115EU (1st Class).
Yes, 75 EUR and 115 EUR are full fares for the route, but there is a limited amount of discounted tickets (SparSchiene) also, they start from 39 EUR (seats). So if you purchase in advance you have a chance to catch those.
And no, train 406 permanently does have Austrian couchette car Wien-Warsawa (carriage #352) and Polish sleeping car (#350). The only inconvenience is that OeBB online ticket selling system can sell only seats, but not couchette or sleeping car for the train you want. As result reservation should be purchased already in Austria from a ticket counter. Or you can actually try to contact OeBB directly, they might be able to book you SparSchiene+sleeper reservation at the same time.