Ok, if you can boot in to your linux install, look in /boot/grub for a menu.lst file (you probably have to be root in order to edit it...) or look in your /etc folder for the menu.lst file.
In that file look for a section that looks like:
Code:
# Below needed only for people who dual-boot
title=Windows NT Workstation
root (hd0,5)
chainloader +1
If it is there, then grub is configured properly. and it should work. Also, is your windows install on the first bootable partition? (Use fdisk to check that). Windows is picky when it comes to which partition its on...