I think that the LegacyURL field is something for a specific site that accidentally got put into the main codebase! :-P

Are the old URLs in any consistent format? Your two basic solutions are setting up RedirectorPage pages with the old URLs, if the are of the form http://www.mysite.com/(url)/

If they are mostly in a couple of directories, you could set up director rules that point to a custom controller that does the redirection.

For example, if you have a bunch URLs of the form http://www.mysite.com/products/(XXX).html,

you could set up a director rule

'products/$ProductURL' => 'ProductRedirector'

and then make a class

class ProductRedirector extends Controller {
function index() {
// do something with $this->urlParams['ProductURL'];
}
}