Think you might get a better answer on Mandriva's forum.
What do you want to delete? The Mandriva install? If so you could just re format that partition as NTFS, that will delete it.
Alternatively, doesn't Mandriva contain a partioning tool? If so that should see both your Linux install and Windows.
Sorry, I'm not really clear what you want to do. If you could post a snip of Disk Management and be more explicit it'd be good