If you are working with a master/detail control, check out the InfoPath Dev Example titled, "Select a Master Table Row via Code". But I don't know that this will select it for editing.
If you are working with a normal table, then you will need to select a control within the table, and I'm not sure that you can do this at all.
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Greg Collins [InfoPath MVP]
Please visit:
http://www.InfoPathDev.com
Is the a way, in script to change the focus to the previous row in a
repeating table?