To completely remove Win XP and install 7: back up any important data, then boot from the Win 7 install disk, and when you get to the step to select a partition, unpartition all partitions that exist on the drive, which will delete everything, and install on the unpartitioned space. Allocate all available space to the partition that Win 7 creates and allow it to format the space. Win 7 will then install and boot up.