Please don't panic. It's unlikely that you've lost anything. It's probably very simple to resolve.
1. You definitely want grub.
2. The only issue is to (re)configure grub so that it finds your Windows partition and can boot from it.
1. Look here:
<= This is good background, but unfortunately we're past that point now
You might want to go back and install EasyBCD after everything's working again, though!
<= Less info ... but more applicable to your immediate problem
2. Boot to Linux.
Post the output of these commands:
su - root
fdisk -l /dev/sda
fdisk -l /dev/sdb
3. Once we know exactly what disk Windows is on, it should be as simple as editing "grub.conf" and rebooting.