You are using the same vmlinuz and initrd.img for Mandriva 2008 and Mandrake 9. Also you are using root=/dev/hdb1 for Mandriva 2008 so you should also use /dev/hdb7 for the Mandrake entry.
Try using the modified menu bellow (don't forget to copy vmlinuz and initrd.img from Mandrake's /boot to Mandriva's /boot and renaming them to vmlinuz-mdk9 and initrd-mdk9.img)
timeout 10
color black/cyan yellow/cyan
gfxmenu (hd1,0)/boot/gfxmenu
default 3
title linux
kernel (hd1,0)/boot/vmlinuz BOOT_IMAGE=linux root=/dev/hdb1 resume=/dev/hdb5 splash=silent vga=788
initrd (hd1,0)/boot/initrd.img
title linux-nonfb
kernel (hd1,0)/boot/vmlinuz BOOT_IMAGE=linux-nonfb root=/dev/hdb1 resume=/dev/hdb5
initrd (hd1,0)/boot/initrd.img
title failsafe
kernel (hd1,0)/boot/vmlinuz BOOT_IMAGE=failsafe root=/dev/hdb1 failsafe
initrd (hd1,0)/boot/initrd.img
title windows
root (hd0,0)
makeactive
chainloader +1
title linux Mandrake 9.0
kernel (hd1,6)/boot/vmlinuz-mdk9 root=/dev/hdb7 devfs=mount hdc=ide-scsi quiet vga=788
initrd (hd1,6)/boot/initrd-mdk9.img