Stragety to archive old site

[bluenoser]

I am looking to upgrade my PHP-NUKE site to vBulletin, however I get a lot of traffic from the SEs so I would like to keep all of my old URLs active, they have already been mod_rewrite-ed. I am not sure what the best way to accomplish this is, can I simply change some settings and install my current site in a archive directory but keep the existing mod-rewrite? Will that cause problems?