rebuilt ECm

hello I'm changing out an ECM and was wondering what can i expect when i try to start it. i've heard that it might need some kind of programming,but will it run and start. this was diagnosed as a bad ECM in my son's 2000 sentra (http://www.nissanforums.com/b15-2000-2006/154090-rebuilt-ecm.html#),so we're getting his rebuilt. $225.00 instead of $600 at the dealer. thanks for any info. Randy
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u will just have to drive it so computer can re-learn all of the cars habbits:smokin: