Thanks for all the input! Implementing what has been suggested (and formatting a bit), I have:

LOCAL lcName
lcName = "John Q. Public"
loForm = CREATE("TestForm",@lcName)
loForm.SHOW(1)
ACTIVATE SCREEN
?lcName && This has to be the value typed into the form

DEFINE CLASS TestForm AS Form
AUTOCENTER = .T.
WIDTH = 150
HEIGHT = 74
ADD OBJECT txt1 AS TEXTBOX WITH ;
HEIGHT = 22, ;
LEFT = 10, ;
TOP = 10, ;
WIDTH = 130
ADD OBJECT cmd1 AS COMMANDBUTTON WITH ;
CAPTION = "Exit", ;
HEIGHT = 22, ;
LEFT = 45, ;
TOP = 40, ;
TERMINATEREAD = .T., ;
WIDTH = 60

PROCEDURE INIT
LPARAMETER p1

THISFORM.ADDPROPERTY("Test",p1)
THIS.txt1.CONTROLSOURCE = "THISFORM.Test"

ENDPROC

ENDDEFINE

This doesn't work. The value of the textbox is "John Q. Public" when the form is SHOWn, but user input does not change the value of lcName.