The First Home Owners Grant will be phased down to its original amount over six months:

For eligible first home buyers entering into contracts between 1 July 2009 and 30 September 2009 (inclusive) the First Home Owners Boost will continue to provide $7,000 for the purchase of established homes and $14,000 for the purchase of new homes. In combination with the existing $7,000 First Home Owners Scheme grant, this means that first home owners will receive a total of $14,000 for established homes and $21,000 for new homes.

For eligible first home buyers entering into contracts between 1 October 2009 and 31 December 2009 (inclusive) the First Home Owners Boost will provide $3,500 for the purchase of established homes and $7,000 for the purchase of new homes. When combined with the existing First Home Owners Scheme grant, this means that first home owners will receive a total of $10,500 for established homes and $14,000 for new homes.

Source: Treasury