I've now done a few tests, which I hope
will give a clue to the problem. I didn't try the Ubuntu 8.04 drive
alone, as it doesn't have a bootable partition.

Firstly, the GigaByte GA-7N400 Pro2 Mobo has the following booting
options in its CMOS HDD-0 ... HDD-3, SCSI, and various other devices.

It has two PATA sockets, and two SATA sockets. There are also another
two PATA sockets, which AFAIK are used for RAID setups. The user manual
doesn't say which boot option to use for serial drives, but it seems to
be HDD-3.

Running Gparted shows the first PATA drive sda ... sda1 FAT32,
boot,lba. sda5 NTFS, sda6 NTFS

The second PATA drive sdb ... sdb1 ext3 lba, sdb5 swap.

The first serial drive sdc ... sdc1 fat32, boot,lba sdc2 NTFS

The second serial drive sdd ... sdd1 NTFS, boot sdd5 EXT3, sdd5 swap

sdd has the new installation of WinXP, which won't boot. Ubuntu 10.4 on
this disk boots OK. XP on sda and Ubuntu on sdb are also OK.

With all the drives connected the same results are obtained when the
CMOS is set to HDD-2 or HDD-3.

When I try to boot XP on sdd I get the message "Windows NT found only 0K
of low memory. 512K of low memory required required."

With the SATA drives removed CMOS set to HDD-0 .... blank screen

HDD-1 ... message displayed - "No active partition"

HDD-2 ... message displayed "Error No such device" followed by a long
string of about 36 characters containing letters, numbers & dashes.

If I just have only the SATA drives connected, and the CMOS set to HDD-3
then the new installation of WinXP boots OK, without the grub menu being
displayed.

Hoping this may give a clue to the problem, and looking forward to any
help or suggestions.