I post this as help, but I'm a newbie, so I STRONGLY suggest to hear someone else before to do anything.
I am a dual-booter too, and in the past I reinstalled Windows a number of times. I have GRUB as bootloader, and each time Windows overwrited the Master Boot Record with its bootloader. So, having more than one Linux partition installed on my system, I used installation disk to reinstall one of the distro with grub, and then I restored the previous menu.lst in /boot/grub.
This isn't a good way to install GRUB, I know it, but this should mean that you could use your Windows CD to do whatever you want, then reinstall GRUB (in another way than I did that time), and have back your system working.
To install GRUB from your system when only Windows is working, I think the best way is to use a Live distro able to do this. For this topic, alas, I have no suggestion...
A thing to be keep in mind is that, in my sistem, GRUB is installed in MBR. I don't know if your system is different.
Remember the first sentence of this post!
Last edited by WhyNot?; 05-16-2006 at 04:52 PM.