Tax Return 2005 in 2006?

I’ve yet to file a tax return for the 2004-2005 tax year. That done I’ll be faced with a tax bill I’ll find difficult to pay in one lump sum. The coward in me wants to put it off until next year when I’ll have a little more money behind me.
My question/s. Can anyone advise the penalty for missing a tax return for any given year. And will the tax department allow instalment payments of tax owed? I’m assuming they will but would like some confirmation and/or any personal experience of this.
Thanks.