How to have node id value set depending on some other id?
Take a look at migrate module and this hands-on guide (disclaimer: I work for that company, so to balance: lullabot's guide ) Both are good to understand everything that's necessary for what you asked.

You might want to consider creating a field_old_node_id field to ease on the transfer if you can't set the ID through this, and use Pages module to create a separate /node/%nid page that uses that field instead to display the node.