Dual boot between Ubuntu and two Windows partitions (Win XP, Win XP 64-bit edition)

[BenoitL]

Hi, 

I'm trying to achieve the following on a new AMD Athlon 64 laptop
(Fujitsu-Siemens Amilo A 1630):

There is a 40GB disk on which there are currently:
- The original Windows XP partition (10GB)
- A partition for Windows XP 64-bit Edition (5GB)
- A partition for shared data (15GB)

I want to set up Ubuntu (wharty-x64) on the last 10GB. I have read on
http://www.ubuntulinux.org/wiki/WindowsDualBootHowTo that it was better to use
the NT boot loader to start Linux than the reverse but I'm not so sure about
that anymore.

My first try was to set Ubuntu on a primary partition at the end of the disk,
using the automated install tool. After a default installation, Grub took place
on the MBR (hardly giving me any choice), didn't detect any of the Windows
partitions and didn't start at all (freeze at boot time). Restoring the MBR
wasn't enough to make Windows start and I had to reinstall both of them.

I then tried to put Ubuntu in hand-created logical drives located in a secondary
partition, just after the first 10GB partition. It worked fine as far as Ubuntu
is concerned (well it was still missing a module required to start XFree,
probably related to the ATI Mobility Radeon 9700 but I think it may be fixable),
but it still took my MBR without detecting any of the windows installations.
Restoring the MBR allowed me to boot into Windows this time, but not in the
64-bit edition. And I haven't been able to make the required linux.bin to dual
boot anyway.

In a third attempt, I launched the installation in expert mode, created /boot,
/, and swap as logical drives in the same place (between 10GB and 20GB on the
disk) and tried to install Grub on the newly created /boot partition (/dev/hda5
at this point). 

What I got is a red screen saying "fatal error running 'grub-installer
/dev/hda5'". I don't know why it doesn't work. My guesses are that it may be
that /boot should be formatted in ext2 instead of ext3, it may be that it should
be on a primary partition, it may be that it should be in the first 8GB of the
disk (I read that somewhere but wasn't that for old hardware? mine is brand
new), or it may be something totally unrelated. At this point I think I need
some external advice.

What do you think should I try now? Accept Grub as the master boot loader and
try to start both XP and XP 64-bit with it (has someone done this)? Rework the
partition scheme again (how)? Any thoughts?

Thanks for your help,
--Benoit