@ Lighthouse: I tried using SARDU for creating multiboot USB.
However, this time too I wasn't able to figure out the step for initiating the process.
Here's the list of confusions that I had to face:
1. What to select if ISO file of an OS is to be selected?
(It shows two options---- "Add extra ISO in GRUB" & "Add extra ISO in RAM")
2.Where to click after selecting ISO files, on "USB Icon" or on "Make USB bootable" in USB tab..
3. Somehow, I managed to make USB bootable with bit of "guess-theory" & when I selected the menu for Windows 8 installation,
the setup displayed an error that some necessary files related to CD/DVD tool were missing.
Don't know what to do..