Dynamic Picklist Sample
Check out this sample to create dynamic picklists on a custom entity
This contains sample code that demonstrates how to implement dynamic picklists on a custom entity. It creates a custom entity named “Dynamic Picklist Test” that contains Industry and Sub-Industry picklist fields. When a value for Industry is selected, the values in the Sub-Industry picklist field are filtered. If there are no sub-industries for an industry, the Sub-Industry field is disabled.
Check out the sample at
http://blogs.msdn.com/midatlanticcrm/archive/2005/12/04/499868.aspx
