I'm running windows XP Pro SP2 at the moment and have been trying for days now to get Ubuntu to dual boot.
I have got windows running on one 500GB hard disk, and I have already resized the partition so there is enough space. I go through the setup (booting from the live CD), I do the partitions manually (4GB Swap and 20GB EXT3 set as root), and it installs fine. When I reboot it doesn't go on to the boot selector, it just goes straight into windows.
I remember when dual booting fedora core 1 years ago I had to change the place where the boot selector was installed (from HD0 to HD1) so I tried that once, and it made it go onto the boot menu at least, but I had to change the boot setup in the command line from HD1 to HD0 to make it boot, and my windows wouldnt boot at all (NTDLR missing).
Any ideas? I've researched for hours how your "meant" to do it, with windows XP still installed but I have followed them all down the the last letter and I still cant get it working.
You could always use a different boot loader that might make things easier. Just make sure you learn how to use it as it can be a bit complicated and you need to know what you're doing so that you don't accidentally prevent Windows from loading.
I use GAG (boot loader). It works well. Once you install a distro enough times, it becomes almost second nature and it is only a matter of determining which partition is what.
I prefer using it rather than worrying about what GRUB is doing.