What is 8MB unpartitioned space in Partition table of Windows Xp?

There is always 8 MB of unpartitioned space so that you can retain the ability to convert the drive to a dynamic volume.

If you have already partitioned the drive from the following operating systems, the empty drive is hidden: MS-DOS

Microsoft Windows 95

Microsoft Windows 98

Microsoft Windows 98 Second Edition

Microsoft Windows NT 4.0

Microsoft Windows 2000