I've had the same problem..
Amd Athlon XP 1900+
512 MB DDR PC2100
Seagate Cheetah X15 36LP ST318452LW
First I did was converting my disk to a dynamic disk, that helped.
Then I installed the pci latecy patch, that didnt help.
Then I installed RPP - Raid Performance Patch, it's for raid.. but i've read somewhere that it helps.. (dont know if it helped for me)
Then I installed Ultra160 Driver Release Candidate 1 for my Adaptec 29160N controller.
And offcourse I installed the Via4in1 drivers.
My write speeds are increased.. And I think my scores are normal now right? :/
Sorry for my bad english