Netflow is not suported on Catalyst 3560 switches. Cisco doesn't document it very well as far as I've seen.
Think of Netflow as primarily a router technology. While most switches also route, the access switches (such as 3560 series) don't have the support for Netflow built into them. 4500 and 6500 series switches handle it via add-on to the low end supervisors (i.e. NFFC for some 4500 supervisors) or high end supervisors (such as Sup-720 in 6500's)