|In Excel 2003, if Calculation is set to Manual, you will get the symptoms you describe. The formulae will auto-fill, but the sheet won't calculate the new values.|
F9 forces a calculation and the numbers will update, so I suggested F9 to see if that would work. That would have led me to conclude that Calculation is set to Manual.
Since I don't have 2007, the only things that I can suggest is to check the Calculation setting to make sure it's set to automatic and to try some other formulae and see if they udpate the values as expected.
Let us know what you find.