Have both on one single SATA-disk.
First installed Windows7 and afterwards Mandriva 2009.1
No problem at all, until................................
Until i had a package of updates for Windows 7, after rebooting GRUB was gone.
That is, GRUB went like a flash through my screen, and the system rebooted, and rebooted, and.......
Had to use the Mandriva installation DVD to repair GRUB.
Everything just fine now, but didn't try to boot Windows 7 again, for being afraid of new damage to GRUB.