GRUB question
 

a)What is the use of sudo grub-install /dev/hda ?
b)Is there any difference while using normal grub configuration like doing steps
1. sudo grub
2. find /boot/grub/stage1
3. root(hd0,0)
4. setup(hd0)

So can anyone give precise difference between a) v/s b)

You should find that grub-install is a script (in my case in /sbin). Have a look at the script to see what the differences are. The script is distro dependent as I recall.