Format my hard drive under Windows XP

There are several ways to format in XP:

During install
Using Diskmanagement under administrative tools
Using the recovery console
Using start run cmd then the format command.
Right click on the drive in explorer and select format.
Using a Win98 boot disk
Note: WinXP will not let you mess with the boot partition or system partition since both contain items required to boot and run WinXP. Thus, you should use the install process to format system and boot drive.

Here is the easiest way to perform a "Clean Install" of XP:

Using Windows XP CD:

Insert your XP CD in the drive while running your current installation of XP.
You will be given some options here. You can select:
Clean Install
New Installation
Advanced
...and others I believe. But since this tutorial teaches a Clean Installation of XP, select "Clean Install".

Put a checkmark in the box to "designate where you want to install XP" (or some such dialog). Typically, you will choose to install XP on your C: drive.
Next, you will need to select the file system you wish to use. I recommend selecting NTFS as it is more sucure than the FAT32 system.
Setup will then format the partition you chose and then you can install XP clean on that partition. Be sure that if you have more than one partition, you select the correct one.
Install your Windows XP Operating System.
Using Windows 98 Boot Disk:

Get yourself a Windows 98 boot-diskette with fdisk. Delete all partitions and THEN boot from the CD. If XP's setup finds formatted partitions, it proceeds without user intervention. If it doesn't find any, setup will prompt you for partitioning and formatting.

Using Floppy Drive:

If you are not able to boot from your CD-ROM, try changing the boot order in your BIOS so that your CD-ROM boots first. If you happen to have a machine that doesn't offer a bootable CD-ROM, you can create the 6 boot discs (below) to allow booting from your Floppy drive.

Windows XP Professional Utility: Setup Disks for floppy boot install
(requires 6 floppies)

Windows XP Home Edition Utility: Setup Disks for floppy boot install