As an executor of your mother's estate - you need to be familiar with the IRS publication 559 - http://www.irs.gov/pub/irs-pdf/p559.pdf
You are correct - you do not need to file federal estate tax return if the total value of the estate is below $2,000,000 (for 2008).
However - you will need to file final income tax return for deceased - regular form 1040,
and you most likely need to file income tax return for the estate - form 1041 - there is no need to have a separate tax ID for the estate - you may use your mother's SSN for reporting.
While I agree with you hiring a lawyer might be a little expensive - I still suggest to have a professional tax preparer to do the paperwork.
Also you might need to consider filing requirements in your state.
Let me know if you need any help.