Create DropDown in crm isa

Hi,

Iam new to crm isa and we have created a brand new jsp which requires a drop down to be filled dynmically from the backend.

I have created the Business Object,Backend Interface etc which will return me the values and i would capture it in a class called capturaction.java.

I dont know how to trigger and call this action when my jsp page loads.

I can do a form action when iam triggering some action and call the action.

But here i have to fill the drop down with values .Please kindly direct me through this step by step.

Regards

Chaitu