ok, you will need to change your boot order in your BIOS to CD, you must know how to boot from a CD because you have reinstalled your OS before so i can skip that ...
Boot from XP Disk...
Go through your installation BUT STOP when you get to the partition section.
When you have to pick a partition to install on delete the C:\ Partition before installing i think you select it and then press D not too sure! i have not reinstalled for a while now
Now select the blank partition and start to install Windows you will notice that it says formating ... Thats good, that means you have done it correctly ... that will takes ages then your computer will restart and you will begin the installation.
I really hope you understand what i am saying because its really easy if you don't i can find you some websites. As i said its been a long time since i have installed Windows so please stay with me on this one.