Reinstalling windows

I already have my opensuse and vista dual booting, but I want to reinstall Vista from 32bit to 64bit.

My concern is windows over writing the boot loader and not being able to get back to my linux install. How can I prevent this without having to reinstall both Linux and windows?

Thanks

Install GRUB in physical partition and use generic boot code.
Mark the Vista partition active before you re-install it.
Afterwards fdisk and re-activate the GRUB partion.

Alternatively break the current Boot and then repair it after with CD/DVD.

Is the repair with the CD 100%? Or is it iffy?