You could create a linked server, and run a cross-instance query of
Insert Into Target .... Select * from Source Where not Exists ...
Or you could create a DTS package, with connection objects for both instances and a Transform Data task
[Edit] ... Or, if there are no Identity columns to worry about, drop constraints in Prod, truncate in Prod, Right-click on table in DEV and Export to Prod, recreate constraints in Prod.