I need to know how to create the select field in the Task Edit form.
The Task module does what I would like to do with my custom field.

Note:
Using SugarCRM opensource 4.5.1c
Module Builder 4.5.1b

To find:
Click on the Activities tab.
On the side menu click "Create Task"
On the right side of the form just under the Status field.
If you click on the drop-down menu it lets you select which module to choose from.
Click on the Select button and a seperate window pops up with a search form for that module.

Question: How is that done? Me want

I understand that the Activities module has a sub-panel under Account.
Is that the link between Account and Tasks? (Account <--> Activities <--> Tasks)
Can this type of field be done with Studio & Module Builder? Or hacking of the PHP files underneath...