FDISK must be run form a true-DOS floppy boot disk, never in a "DOS windows"
or "command prompt window".
FDISK will NOT recognize an NTFS partition. It will call it non-DOS, or
unrecognizable, or similar.
However, FDISK can delete all partitions on a hard dirve, even if it can not
recognize some/all of them. If you do this, all data will be lost, but this
is OK is you plan a clean install. Note that the installation of XP on a
blank hard drive will automaially offer to create at least one partition,
the one for XP itself.
Be sure to use the latest version of FDISK. Check with
www.bootdisk.com for
a copy an an associated boot disk image.
Alternatively, boot into the XP recovery console from the XP CDROM. It can
also delete partitions. Further, it can then recreate one or more NTFS
partitions (or FAT32, if you prefer).
Links to XP recovery console:
http://www.wown.com/j_helmig/wxprcons.htm
http://www.xxcopy.com/xxcopy33.htm (near bottom)
http://www.kellys-korner-xp.com/win_xp_rec.htm
One other point, XP can not re-partition after it is installed. So, choose
your partitions wisely, before you install. Or, plan on getting a
third-party program like Partition Magic, which can re-partition fter XP is
installed, without data loss.