First, you can format your partitions (except the one where your OS is installed) directly from your desktop. Click MY COMPUTER, right click on your partition and select format.
You can also partition the old disk using your XP CD. Make sure your CD-ROM boots up before your HDD in your BIOS, insert CD and start computer, follow the prompts (XP CD is bootable) This will allow you to delete all partitions, repartition your drives, format your drives with fat32 or NTFS and reinstall XP.
Once evertything is installed the way you like it, You should do a ghost of your computer since this takes a few minutes to reinstall instead of going through the process of reformatting and reinstalling everything.
My gaming machine:
P4 2.8 GHz
2 X 512 MHz PC3200 in dual DDR mode
Intel D865PERL MOBO
integrated 6.1 MAX audio
Logitech duo MX mouse and KB
ATI RADEON 9800 PRO