You will need a Windows disk unless you've manually installed the Recovery Console (you probably haven't) because you need to give Windows back control of the Master Boot Record. Right now it belongs to GRUB, and GRUB ain't finding it's /boot partition.
Once you have a disk (I
believe you can borrow one because you are not actually installing Windows with it, and thus it is not illegal

), set your computer to boot from CD (in the BIOS), and follow the on-screen directions to get into Recovery Mode.
Instructions to do this (Choose
Start the computer and use the Recovery Console Link)
then run the following commands in order:
FIXMBR
FIXBOOT
BOOTCFG /REBUILD
then reboot. That should have you booting into Windows.