First of i would like to thank you very much for your reply and valuable guide.
I downloaded gparted iso file, burnt cd and booted pc from that cd. I got options there to resize the partitions, but unfortunately in the ignorance i deleted LVM2 partitions. Now when i reboot the pc it goes to grub> prompt.
I thought that probably some problem has been occured with grub, so i inserted the RHEL5's first cd and "linux rescue" ... i got command prompt after chroot /sysimage/mnt (i am just remembering what exactly i gave there). Now, when i says grub-install /dev/hda then it is saying there is no device.
It is my home pc, so i just use for learning, testing and meanwhile for damage too...!
Kindly guide me how to recover the LVM and/or grub installation.