If I have the 2004 income statment for a firm along with the
12/31/2003 and 12/31/2004 balance sheets, how would I calculate net
capotal spending?

Oneten --

Merrill Lynch
"How to Read a Financial Report"
http://philanthropy.ml.com/ipo/resources/pdf/howtoreadfinreport.pdf

Best regards,

Omnivorous-GA

I'll assume you mean total capital spending, (not net).  You can not
get an exact number if these are the only financial statements you
have available.  The full calculation to get from 03 to 04 capital
asset accounts is
03 capital asets, less depreciation plus capital spending, plus assets
acquired in FY 04, plus depreciation on capital assets purchased in
04, = 04 capital assets.
Since you don't know assets acquired by acquisition or the
depreciation within 04 capital spending the closest you can get is (04
capital assets - 03 capital assets + depr = Capex)
The importance of the missing data is dependant on the nature and
actions of the company.  Do they make substantial acquisitions?  Is
there business primarily longer life assets (like roads, long life
equipment etc) or short life (computers, software etc.).  Also did the
company have any asset writedowns in the year.  If so these should be
added to get your capex number.  I hope that helps.