U do not have to reinstall linux if your grub is lost especially due to windows installation.
just follow these easy STEPS and hope u will recover:
Insert bootable cd-I or DVD of your linux
Type: linux rescue
Follow instructions for keyboard and language settings
Then you will see the shell prompt
Type: chroot /mnt/sysimage
now you will get the grub prompt as grub>
Type: root (hd0,5) // hd0 means harddisk 1. if you have on HDD 2 you need to type hd1 and so on. later number (5) implies partition of selected harddisk where you have linux installed previously. It varies with machine enter the partition where you have your linux partition.
setup (hd0) // same HDD as before, its hd1 if your linux is in 2nd harddisk
now exit from the grub and from the shell too. After restarting your grub gets recovered, hopefully