Hi Alberto,
First it's better to provide some info about 3 packages you want to run sequentially...
Second, the info about package link is in: EPMofc_10_user_en.pdf (http://help.sap.com/businessobject/product_guides/boeo10/en/EPMofc_10_user_en.pdf)
40.5.4 Defining a Package Link
Vadim