dynamicly populating a dropdown box

i spoke too soon on having everything i need.
given i have the data needed to populate a drop down box dynamically what is the expected return value and how is it populated? i noticed this example: http://www.gravityhelp.com/documentation/page/Dynamically_Populating_Drop_Down_Fields
but this is using a filter. i would prefer to do it similar to the way described here; http://www.gravityhelp.com/documentation/page/Using_Dynamic_Population
using a hook.
Thanks
Kim