I allmost resolved the problem, I need only one thing more...

When I use

oExcel = createobject("Excel.application")
with oExcel
.Workbooks.Open("C:\estaib\archivos\abril2006.xls")
.visible = .t.
I´m sure that the computer has intalled the software, but what happen if the compuiter doesn´t has the Excel installed, how can I check it...???