Hi Edgar,
You can have look at my 'rep2excel' tool here in downloads.
It is class object having most of common excel writing tasks wrapped into simple methods calls, leting you write excel file as u wld write 3d array.

Belowe method call , after excel wrapper class has been instantiated
wld do task you mentioned;

oXl.make_cell(1 ,9 ,1 , DATE(1990,01,01) )
*lParameters nSheet,nRow,nCol , YourValue

There are many other calls for writing entire tables into specific section of excel sheet , arrays , delimited strings, drawing boxes, painting areas
seting formulas etc.
.
oXl.table_in_section(2,10,10 , MyTable)
oXl.array_in_section(3,10,10 , @MyArray)
.
etc.

If you want to write fully blown report in code (with grouping, headers footers etc) then you could also see/use 'CodeRep' tool which also uses the same excel driver to produce excel ouput.

Both downloads are free / shipped with full source code and samples.

Rgds++
Sergio