Decide how many partitions you "need", just just a random thought of how many you want. For most purposes, there isn't a need for more then 2 partitions. 1 for Windows, 2nd for data.
All partitioning is also done right from within XP setup program, you don't have to use any other tools or programs. Just tell XP to create a new partition (1st partition, OS) and make it whatever size you need, then have it use the rest of the space for the 2nd partition. Or create a 2nd partition of size, and so on.