From Microsoft Support - http://support.microsoft.com/?kbid=302686
When you choose to run a regular format on a volume, files are removed from the volume that you are formatting and the hard disk is scanned for bad sectors. The scan for bad sectors is responsible for the majority of the time that it takes to format a volume.
If you choose the Quick format option, format removes files from the partition, but does not scan the disk for bad sectors. Only use this option if your hard disk has been previously formatted and you are sure that your hard disk is not damaged.
If you installed Windows XP on a partition that was formatted by using the Quick format option, you can also check your disk by using the chkdsk /r command after the installation of Windows XP is completed.