I installed Windows XP on a fat 32 partition, but before I could finish the instalation, once the computer rebooted to finish installing windows, I just couldn't boot anything anymore. I had Linux installed before without any trouble, but I decided to install windows on the extra partition I had. The message I receive when I start my computer says:

Can't find NTLDR, please restart (or something like that)

How do I fix this???? I think something happened to grub, but I don;t know what exactly. Thanks