Windows usualy installs its bootloader in the MBR. Sometimes it happened to me that on a reinstall it would install the bootloader in another primary partition ( in fact that was the reason so now I only use a primary partition setup and the rest in the extended one).
So here is how I did it when I was dual-booting:
Windows was to be installed first onto a primary partition at the begining of the hard drive.
The rest of the hard drive is taken up by the extended partition.
In the extended partition I would have a FAT32 for use by both systems and the rest for use by linux(swap, boot partition, root partition and home partition(optional)).
The linux boot loader was to be installed in the linux boot partition(32MB) in the extended partition and not in the MBR because it would replace the windows boot loader.
You might ask "So what?" but in fact to boot Windows, grub chain loads the windows boot loader, meaning it does a few optional and some required tricks and passes the control to the windows boot loader.
Then the boot partition is made active.
You edit the grub menu with the windows boot partition (the first primary one in my case) and also boot the linux kernel from the linux boot partition(the one with grub
) and tell it the real root partition(the linux root partition in the extended partition).
Then you can easily boot any of the OS's with no fear of ruinning the windows install.
Just my tried and worked, nothing more. :-D