FeatLayer.Where = "POP2000 > 500000 AND POP2000 < 1000000";
Look at the Where property of a FeatureLayer. Documentation says 'Any legal SQL where clause operating on the fields in the layer is allowed' so you should be able to do something likeFeatLayer.Where = "POP2000 > 500000 AND POP2000 < 1000000";
What's considered legal SQL statement will depend on the underlying data source.
TG