Ok, Are you wanting to start over and format the entire drive to reinstall windows? If so, boot from your windows Xp disk and follow the instructions on formatting and then creating a new partition to install the OS on.
Just put the windows CD in and boot from it. When you get to the part where it asks you where you want to install windows, you can select your current partition, and select D (I believe,) to delete your current partition. Then you select the unpatitioned space, and create a partition. Then if it asks, you want to format the patition in NTFS, but do not choose the quick format. It should then procede on it's merry way.
Also put OS on one partition Programs on the other and Pics, Movies, Music on the 3rd partition. Partitioning won't improve performance unless your short stroking, however it will make it easier to manage, organize, backup and defrag your drive.