Hi Andy,
Any lower end switches like 2950,3550 and 3560 and 3750 does not suppor NetFlow as its a hardware limitation.
The Catalyst 4500 series switches do support NetFlow Statistics Collection, however, to use the NetFlow feature, you must have the Supervisor Engine V-10GE (the functionality is embedded in the supervisor engine), or the NetFlow Services Card (WS-F4531) and either a Supervisor Engine IV or a Supervisor Engine V.
Cat6500 also supports NetFlow.
HTH
Ankur
*Pls rate all helpfull post