Having trouble using UNetbootin to create a bootable USB Drive ..

Hey all .. Well if you've read my last few threads then you know that I'm trying to create a backup disk image of a netbook I recently received ..

Anyways, (long story short) I'm trying to make a USB Hard Drive I have (a 2.5" internal 80GB Hard Drive in a 2.5" enclosure) bootable, from which I can load a Linux based PE to create backup images, etc .. I can't get this step done for some reason ..

Here's what I'm doing exactly:

1) I format the said USB Hard Drive to FAT32 ..
2) I download the CloneZilla ISO image (or the Linux image from Macrium Reflect - procedure is same for both) which are bootable CD images ..
3) I run UNetbootin, select the ISO file, and indicate the drive letter of my USB Hard Drive, and start the procedure ..
4) UNetbootin now says that my USB Hard Drive is 'bootable' ..
4) I restart my computer and try to boot from the USB Hard Drive ..

All I get is a the blinking underscore ...

Please note that in UNetbootin, I had to check 'Show all drives (use with care' option to see my USB Hard Drive's letter in the list .. I also indicated my USB Hard Drive as a 'USB Drive' in the list, and not 'Hard Disk' ..

What am I doing wrong above ?

Please don't deviate from the topic .. I'm using a USB drive and not CD/DVDs as the netbook that needs to be backed up doesn't have an optical drive ..

Also, I can't use Windows 7's built-in backing up features as they don't support backing up hidden partitions ..