these procedures have been tested out on ubuntu and linux and i am sure it can well work with all other distros as well;;

so here we go;;

Preparing the files and USB flash drive:

1.)First ,u need to format the USB drive in Windows in Fat32 format only!!, the ntfs format will not work   

2.)Download &install 7-zip ,use it to uncompress the iso file . u can also use winrar but use it to be on safer side..
 
3.)Download Syslinux,( bootloader)  and then extract and rename it to a  folder named “syslinux”.
 
4.)Open a command prompt (on the Start Menu under Accessories, or run “cmd”) and cd (change directory) to the syslinux folder:
Run this command to install the syslinux bootlader to the thumbdrive:
syslinux -ma f: (where f: is the letter of your USB drive)
Now  extract the Ubuntu ISO using 7-zip or winrar( i mostly prefer 7 zip as it is most reliable)5.)The preparation is done! You should now have syslinux installed on your USB thumb drive, and a folder called Ubuntu-8.04-somethingorother on your Windows desktop. Now it’s time ot create our bootable Ubuntu LiveUSB Stick!

6.)Drag all of the files you just extracted from the ISO into the empty USB drive.
Move everything from the isolinux folder into the root of the drive.rename the isolinux.cfg to syslinux.cfg

7.)Eject the usb drive, then insert into the pc u want to install unix distro(ubuntu or any other distro).make sure to boot the pc using usb drive.it can be easily done by selecting the usb drive as first boot preference in bios of the pc(remember to plugin ur usb into the pc before starting the computer, then goto bios for making the usb drive boot preference selection.)