Restricting node reference values to owner
If I understand you right, you can use a View as the source for the nodereference widget, and give it appropriate filters to only show nodes of a certain type authored by the current user. To use a view (assuming you have Views installed and appropriate perms) you can


edit the nodereference by going to Content management -> Content types -> Edit [whatever content type] -> Manage fields -> [whatever field name];
in the fieldset Global settings click to expand the fieldset Advanced - Nodes that can be referenced (View);
select the appropriate view in View used to select the nodes;
if you want to use arguments you can specify them in View arguments.