InfoPath Dev

I have a repeating table, that each time the form is saved (the form will be opened and updated repeatedly) I want the existing rows in the repeating table to become read only when the form is opened again and only the newly added rows to be editable.  I tried adding a date/time value to the repeating table and comparing this with a date/time hidden value with a defaut value of now(), and comparing the two, for example if date1 < currentDateTime, set all the fields in the table to read only.  Not working.  Any suggestions?

Thanks 

What if you gave each row a hidden isReadOnly field with a default value of false, and set this field to true when the form is opened, then use that to control the conditional formatting?  That should work.

Now why didn't I think of that? Thanks so much, works like a charm!