Who said grub cannot installed with only windows?
GRUB can be surely used. But, to boot windows grub always uses a chainloader even when dual booting with linux. See this *www.geocities.com/lode_leroy/grubinstall/
Any problem using ntldr? You can always dual boot with ntldr. Here's one reslut from google search *vlaurie.com/computers2/Articles/dualboot.htm, you can search for more.