Pretty much all tickets are only valid for a year. They do this so that any given date only has to appear once in their systems. It makes managing the data sets much less complicated for the airlines.

Even if you could book a ticket for a full year, you'd basically be paying the walk-up price at the time of booking since you'd have to wait until your day of departure to get the return one year out.

What you can do is book today for a June 2009 departure and a March/April 2010 return. Once the return inventory for the June 2010 return becomes available you MIGHT be able to change the return date to your desired date, but only if that date is within 365 days of the outbound. You'd pay the change fee and any fare difference but that might still be less than the cost of two one-way tickets.

But you still have to deal with the one year max validity on the ticket.