I'd try and repost on the centrelink/tax questions sticky. I'm assuming they would look at total income for 2005/2006 financial year which means including what you have already earnt while working.
Family Benefit Part A's maximum is $117.60 and starts reducing if the SAH parent earns more than $4000 and something per year (look at centrelink for figure).
Family benefit Part B is on total combined income and cuts off totally just above $92 000. $44 (from memory) is the minimum amount.
You may also be able to get rent assitance if you're renting.
Definately look at centrelink sticky though as they should be able to help you much more. Also look at the centrelink web sitecentrelink
If you still need extra money is it possible to work in the evenings or weekend when your DP is home?