my current primary partion is ext3 with linux installed in it . i want to create a pr
 

my current primary partion is ext3 with linux installed in it . i want to create a primary fat partion for windows.how acn i do it from linux.yes how can i reinstall grub.

See the Linux System Administrators Guide, chapter 6, section 7, for information on partitions. You may not need another primary partition, just an extended partition, sub-divided into a bootable windows partition. The fdisk and cfdisk utilities can be used to accomplish that task.

How to re-install grub? Search these forums. There are many posts regarding that issue.