Basicly the only difference is that the quick format does not scan the hd for bad sectors.
Here is what microsoft sez.
"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."