The Outsider <no@spam.here> wrote

That is your problem, doing that before installing 48 bit LBA support.

Its better to slipstream SP2 onto the XP distribution and install from that.

You dont need to do that registry entry with SP2

Where ?

Because you had created that partition using
PM without 48 bit LBA support installed.

With 48 bit LBA support enabled.

Start over. Slipstream SP2 onto the XP distribution,
http://www.neowin.net/forum/index.php?showtopic=223562
boot that CD, deleted all partitions on the drive and
then install XP on that drive in its own partition.