[gentoo-user] bios+gpt+grub2 boot windows

[东方巽雷]

I format my hard disk to gpt.Then create a 1M partition at the header of
hard disk ,add "bios_grub" flag.I can install and boot gentoo,debain and
archlinux,but have no idea how to boot windows7 and 8.When I boot win7 or
win8 from usb,it always complain the gpt partition and cannot install.What
should I do?