Unfortunately, the agent that told you that you can't check on award availability was wrong. For domestic flights, you can check on united.com. For international flights, you can use the PDA application at
http://www.ua2go.com/htm/mpavail.htm
This is the way FF programs work. You can book capacity controlled saver award seats on United 330 days in advance of the flight, and even then, the flights you want may not be available. Or you can book standard award seats on United for more miles and get a seat anytime one is available for sale. Flying on award tickets requires a lot of advance planning.
Once you transfer the points to United, you can't transfer them back to Marriott Rewards.
-David
[This message has been edited by LIH Prem (edited 08-20-2001).]