1) Download http://ext2fsd.sourceforge.net/ . This is a system driver for Win32 for reading and writing to ext2 partitions. It even has an option to mount partition as a normal windows drive.
2) Use any tool for windows to partition your harddrive and make one more small partition... like 1gb ext2 type.
3) mount the small partition with mount from ext2fsd
4) Download grubinstall. This is a grub installer for win32.
5) Install grub
6) Download gentoo minimal installation cd (or universal one, but then the small partition I was talking about should be bigger)
7) Unpack the .iso in the mounted small partition
8) Reboot and choose GRUB
9) Type in
Code:
root (your hd number, small_partition_number)10) You've just booted the installation disk using the small partition.
kernel /isolinux/gentoo initrd=gentoo.igz root=/dev/ram0 init=/linuxrc looptype=squashfs loop=/livecd.squashfs cdroot=/dev/small_partition dokeymap initrd /isolinux/gentoo.igz boot
Continue the installation as a normal gentoo installation.
From http://forums.gentoo.org/viewtopic-t-389471.html