One of my friends just screwed up her linux boot record by installing M$ Windows 2000 Professional on top of it. Luckily she didn't delete any of her partitions. This blog is for her and others who have done similar mistakes, unknowingly.
1) Reboot your system using the Linux bootable CD.
2) Choose "Rescue system" or similar option that would take you to a temporary shell.
3) Follow the steps mentioned in the link given below.
Well, I thought of writing all the steps to setup grub again, however, a google on "setting up grub" revealed this link here, which explains the steps to install grub quite comprehensively.