System re-instalation & Grub problem

[Self-Defence]

Hi,

I've got a cuple of systems installed on my machine, but somethings seems to have gone wrong with the windows system. And rather than trying to fix the problem I'd like just to re-install the system.
Here's how the hdd is set up:
/dev/sda1 (ntfs) <--- WinXP Pro
/dev/sda2 (fat32) <--- Data Partition
/dev/sda3 (ext3) <--- Ubuntu (the primary sytsem)
/dev/sda5 (swap) <--- Swap
/dev/sda6 (ext3) <--- Fedora
/dev/sda7 (fat32) <--- Win98

Ubuntu was the last system to be installed and so the Ubuntu Grub is used as the boot agent, whitch sutes me just fine since it is simple and elegant.
But the problem is if I re-install WinXP the boot loader gets replaced by the win. boot loader. Becouse previously on another machine when I tryed to re-install the Grub of Ubuntu I was unsuccessful.
So my question is, does anyone know a way that I could re-install the win. system and still keep the current Grub boot loader?
Would it work if I made a backup of the current MBR and after re-install of the win. system just simply restored the MBR backuped before the re-install?
And if so how can I backup and restore the current MBR?

Thanks for the help

[devils casper]

if you re-install Windows, MBR will be over-written. after Windows installation, either re-install GRUB through Ubuntu LiveCD or 'dd' command. both methods are easy but you have to be very careful while executing 'dd' command.
first create 'image' file of MBR. boot up Ubuntu and execute this code in terminal.

sudo dd if=/dev/hda of=mbr_image bs=521 count=1

this command will create an image file 'mbr_image' of Master Boot Record.
after Windows installation, boot up through Ubuntu LiveCD and execute this command

dd if=<path/of/mbr_image> of=/dev/hda bs=521 count=1

i am repeating again, be very careful while executing 'dd' command. a single typo will hose Partition Table and Master Boot Record.
i would suggest you to create mbr_image and try grub re-install through usual setup/grub-install command. if it doesn't work, only then execute 'dd' to paste mbr_image in MBR.





Casper

[Self-Defence]

devils_casper -> thank you.

I reinstaled windows and then booted from the live cd and tryed to install grub. But that didn't work. So I tryed the dd method. Thankfully I made the bacuk image befor installink.
But it seems that that all my efforts were for nothing the win. system still seems to be crashing at boot. But that another problem all tougether.

Thanks for the help very much.

[devils casper]

what did you try to re-install GRUB? whats the error message? as i mentioned earlier, its easy to re-install GRUB but you have to tweak a little bit.






Casper

[Self-Defence]

Well I had to reinstall the win. system and railroaded grub again. So I put in a live distro and booted it up and just installed grub again. It worked fine for the win system that I reinstalled, but all of the other systems still woulden't boot. So I fixed grub entries manualy and got ubuntu to boot and fixed menu.lst.

Anyway all works now, so thanks