I don’t know what your intended result is, but it sounds like you can use the lookup filters that exist on reference fields.

I didn’t know they existed for 6 months but now I use them like crazy.

Thanks Moshe, but I am looking for how to do this for non-reference fields. The two examples above show how to create picklists from ‘normal’ fields, I want to do similar, but as a lookup.

Ross  - to be clear,  you would like to have a picklist field rendered so that it looks like a reference field lookup?  (Essentially presenting a type ahead field?).   Is that what you are after ?

Close, but I want to use a ‘normal’ text field, like in the two examples I gave. They both give a picklist that the selected item used to populate the text field. I wish to do something very similar, but with a lookup or type ahead.