Do you want this to happen for all new records until the "new" form is
closed again, or until the user makes a different selection from the
original combobox?
If the former, you can get the "new" form to pick up the value from the
combobox on the first form, with code like this in its Load or Open
event procedure. I'll assume that the forms are frm1 and frm2, the combo
box is called cboSetTheValue, and that the new form has a textbox
txtTheValue bound to the field in question.
'Make sure frm1 is open
Dim j As Long
For j = 0 to Forms.Count - 1
If Forms(j).Name = "frm1" Then
'frm1 is open, get the default value
Me.txtTheValue.DefaultValue = _
Forms(j).Fields("cboSetTheValue").Value
End If
Next
If you want the default value to persist if frm2 is closed and
re-opened, or if the database is closed and re-opened, you need to
(a) put code in cboSetTheValue's AfterUpdate event to store the value
somewhere, e.g. in a "Settings" table in the database or in an .ini
file.
(b) have the code in frm2's Load or Open event handler retrieve the
stored value.