How do I set a default value in a popup menu through a script... One of these popup menus uses a value list from another file?

Not sure exactly what you mean here. Maybe you can clarify what this script does and why it is relevent that the value list is from another file.

I'd assume you'd have some tests and if they do not pass the tests then the default action would be "Set Field popupFieldName = the value you want"

As long as the default value is always the same, it doesn't really matter that it is in a value list. Maybe that helps?

The way to set a default value is to auto-enter it when the record is created, or to enter the value with a script at some other time.

I think I need to go back to basics... If I have a popup menu with a list of choices from a value list. Is there a way to select which value is default or more precisely, which value shows up on screen and is used for calculation if no choice is selected?

Define an calculation:

Case(popUpList,popUpList,DefaultValue)

disallow entry into field make it trasparent and put it over your pop-up field

Dj

"I think I need to go back to basics... If I have a popup menu with a list of choices from a value list. Is there a way to select which value is default..."

No, other than entering the default value into the field.

Remember, the pop-up list is just a mechanism for presenting a list of possible values. There is no way to coerce any one value over another in a value list.

"... or more precisely, which value shows up on screen and is used for calculation if no choice is selected?"

This is actually a different question! This is usually achieved by using two fields, one that the user enters into, the other is a calc field that goes something like "If(IsEmpty(UserEntryField), DefaultValue, UserEntryField)".