2007.1 is still in rc (release candidate) phase. When the official release comes out (perhaps by the time you read this)
As root do: urpmq --list-media
urpmi.removemedia media-foo or urpmi.removemedia -a (all)
then visit;
http://easyurpmi.zarb.org/
pick the 2007.1 Mandriva version and then follow the steps. be sure to click the steps.
you will then get commands to add to root which will add new urpmi media for you.
you should be able to urpmi update from there.