I have many One to many forms and the way to do work this is:
In the Data environment I set the relation (it doesn´t be One to many)
ParentTable---->ChildTable

Initial selected area: ParentTable

In the Form:
I put text boxes for ParentTable fields
In the Grid set the same relation than in Data environment but don't set to any Column a Field of the ParentTable

to insert a new record you can use this code:

Insert Into ChildTable(KeyField) Values(ParentTable.KeyField)
Thisform.Grid1.Column1.Setfocus

I hope this help