Andrea,
In the examples that Jeff gave, replace the "53", "55", or "5" used as example port numbers in his commands with the correct ifIndex of each port that you wish to enable sFlow on. You must follow each step that Jeff enumerates for every such port.
On the topic of switch ifIndex values (i.e. 53 in the examples vs. your 48-port switch) you should note that depending upon your switch configuration you could actually have a "virtual" port numbered in the 50s. When a trunk or mesh is enabled on a ProCurve switch that supports sFlow, the MIB variables of the trunk or mesh constituent ports become inaccessible and are replaced by a "virtual" port that is created to represent the entire traffic flow of the mesh or trunk. So in other words if you created a trunk using ports 1, 2, and 3 of a switch the sFlow MIB variables for ifIndex values 1, 2, and 3 would subsequently "disappear" from the MIB and would be replaced with a corresponding set of MIB entries that allow sFlow to be applied to the entire trunk as an aggregate; the new MIB entries would be numbered using an ifIndex that is out of range of the device's physical ports. This creation of a virtual port allows applications to monitor aggregated traffic flow through a mesh or trunk quite simply by having the agent do the "assemblage" of data from the constituent ports within the trunk or mesh. You can determine which ifIndex has been assigned to a trunk or mesh by looking at the ifDescr fields within the MIB-II ifTable.
