This is how I managed to maintain my machine's bootloader configuration (using boot.ini) to dual boot between a pre-existing installation of Windows XP and a new installation of Ubuntu 7.10.
After installing Ubuntu 7.10 to a suitable partition, GRUB installs itself on that disk and takes over the boot process, a bit annoying since I've never been able to get the thing to then boot into my XP partition via the pre-configured menu option presented in GRUB.
But not all is lost. It's easy to get around it (when you know how...)
There are number of ways of doing this and this is the easiest for me.
1. Boot into Ubuntu 7.10 and copy menu.1st from boot/grub and copy it to the root on the XP NT partition (c:\) or if not available a a suitable shared partition that you can copy it from into XP later.
2. Edit boot.ini on the c: drive of the XP/NT partition and add the following line under the c:\grldr="GRUB". I find this easiest to do from within Ubuntu since it will allow a file edit without having to mess with the NTFS file permissions.
3. reset the Master boot record back to using the NT Bootloader. I have a boot/repair CD that allows me to run the DOS/Win98 command FDISK /MBR to restore the master boot record on the 1st disk.
4. Reboot the machine and Launch Windows XP. download GRUB4DOS.
5. Extract the content of the zip file and copy the file grldr to the root of the c: drive
6. Reboot your machine and select GRUB from the Boot.ini menu and it should start the GRUB loader and present the UBUNTU 7.10 Grub menu to launch from!