If you want to preserve your existing Xp installation you need to buy "Partition Magic" here:
http://www.symantec.com/norton/produ...d=sp&pvid=pm80
If you don't mind having to re-install XP you don't need to buy anything. Just boot up from your XP CD, when setup starts delete all existing partitions then install XP on this "unallocated space" (XP will automatically create & format it as a single partition).
One final comment. dividing 40GB into 4 partitions is ridiculous. These days a partition needs to be at least 10GB, and more usually 20GB. XP doesn't have room to "breathe" on anything less. And that slows it down.