You'll use Grub to bless hda2 as the boot partition, and then grub will start windows up when you select it. For an almost identical setup, here is my grub conf file, which should get you going.
default 0timeout 30splashimage=(hd0,1)/grub/splash.xpm.gztitle=Gentoo Linux 2.6.7-r14 Genkernelroot (hd0,1)kernel /kernel-2.6.7-gentoo-r14 root=/dev/ram0 init=/linuxrc real_root=/dev/hde4 vga=792initrd /initrd-2.6.7-gentoo-r14title=Windows XProot (hd0,0)chainloader +1
