Enter Layout Mode and select Set Tab Order... from the Layouts menu.
will this work in rows in portals?
You may need to set up an OnObjectKeystroke script trigger for this. In the script, You'd test the keystroke for any tab or enter characters and use go to next portal row and go to field to move the cursor to the next record and then use exit [ false ] to keep the keystroke from doing it's own exit of the field.
You'd use OnObjectKeystroke instead of OnObjectExit so that you can click other items on the screen without triggering this script.