Hi!
In case you work in a windows environment (and have Excel installed) Win32:: OLE is probably the best way to go.
An excellent introduction can be found here: Using Win32::OLE and Excel - Tips and Tricks.
Once you know the basic principles, the "Excel Visual Basic Reference" will help you in identifying objects and methods (you can find it by opening the "Visual Basic Editor" from Excel, then selecting "help"). You then "just" have to translate the visual-basic syntax to the perl one.

HTH Rata