I have a dual boot Windows & Linux system. I removed the Linux partition, but after that I am not able to go in to Windows XP. It is not booting. It gives me a GRUB error.
I'm not sure I follow, but what do you want to do? If you want to completely remove Linux (sadly), you're on the right path. You just have to boot into your XP CD and let the Windows setup take care of repartitioning and installation. Why do you need Grub?
If you want to use both, Grub is obviously not able to find the Linux kernel that you deleted. The easiest way is to set up your partitions with something like Gparted, reinstall XP first, and THEN your Linux distro (with Grub)from an iso or network.