Hi Valeria
(not tested) but try:
Sub test()

Dim StartLine As Long
With ActiveWorkbook.VBProject.VBComponents("Sheet1").Co deModule
StartLine = .CreateEventProc("Change", "Worksheet") + 1
.InsertLines StartLine, "If Intersect(Target, Me.Range("a1:a100")) Is
Nothing Then"
.InsertLine Startline+1, "Exit sub"
.insertLine,startline+2, "End if"
'....




"Valeria" wrote:

Dear Experts,
I would like to write a macro in a worksheet code of a spreadsheet from
another macro. I have visited Cheap Pearson's page,
http://www.cpearson.com/excel/vbe.htm, which was very useful, but still I do
not understand how to write my code (I am not very good at it! :-)
[...]
Sub test()

Dim StartLine As Long
With ActiveWorkbook.VBProject.VBComponents("Sheet1").Co deModule
StartLine = .CreateEventProc("Change", "Worksheet") + 1
.InsertLines StartLine, _