bwnbwn - 8:10 pm on Sep 22, 2009 (gmt 0)

Just because your changing your technology dosen't mean you have to change the url's
I would keep the url's the same as with the page content on the rebuild. This by far is the best, safest, and continues to pass ALL link juice to the internal pages that are linked.
Done this way I doubt you will see any drop in the SE's.

AnkitMaheshwari is correct Yahoo does not process a 301 good at all and you most likely will lose all the yahoo serp positions.