I would just format the entire drive, you really want your OS to be the C drive. If you just want to delete the XP partition, click start, right click "computer" and click manage. From disk management you can delete the xp partition, but will be unable to merge it into the 7 partition, you will have to make a new partition from it. You can also use a third part partitioning program to delete XP and merge your partitions.