How to uninstall Mandriva and restore Windows 7 Bootloader?
Use windows 7 boot disk, enter rescue mode,
type bootrec.exe /Fixmbr ?
Any suggestion?

You seem to have answered your own question, I think... Or are you looking for a different solution?

You could try to use a GNU/Linux live CD, install ms-sys (many distributions have this in their repositories), and write a new Windows 7 boot sector. For example, you can run `ms-sys --mbr7 /dev/sdX`, where X is the letter of the drive on which you have Windows installed (if you're unsure of this, run `fdisk -l` and look for an NTFS partition that you recognize).

for reinstalling Microsoft and the win7 bootloader
search the Microsoft web site
they have the instructions there ( it is there os after all)
the OLD instructions for xp and the "newer" ones for vista
DO NOT APPLY ,or work for windows7

For windows 7, after bootrec.exe /fixmbr, its bootloader still unrestored.
have to go back to the screen, click Repair, and windows will do something and restored.

Then use ms-sys; it's pretty reliable and easy to use. And here's a post on how to use it on an Ubuntu live CD. Just use the '--mbr7' flag where the author uses '-m' (as I did in my previous post).

did you reformat the mbr ?
microsoft can not read NON Microsoft partition formats

i am willing to bet that Mandriva formatted it to ext3

Umm... The IBM PC master boot record is a 512-byte (1-sector) record with 440 bytes of boot code, a 4-byte disk signature, two placeholder bytes (usually 0x00 0x00), up to four 16-byte partition entries, and a 2-byte (0x55 0xAA) MBR signature (I'm reading this off my wall, lol). The MBR is not a partition itself, and there is no filesystem on a boot sector.

It's the boot code that is OS-specific (or more accurately, boot loader-specific); Windows OSes each have their own boot code, which bootstraps the OS and runs the NTLDR process on the partition marked bootable in the MBR partition table. Mandriva wrote the boot code for either GRUB or LILO (whichever you used) into the MBR; that code would load up the kernel with your initramfs, which in turn bootstraps your system and eventually passes control off to init.

thanks, very helpful