The column headers should be letters after you installed XL2007; that is the
default.
To get numbers and use the R1C1 style;
1) click the Office Button (colourful circle in top left corner of Excel
window)
2) click Excel Options button located at bottom of resulting panel
3) In left panel of next window, click Formulas
4) In the second grouping down "Working with Formulas", the first selection
box is labelled R1C1 reference style
best wishes