Hello,
I'm not sure what exactly do you mean. If you wish to create bootable USB, please consider looking at this page -
http://fedoraproject.org/wiki/How_to...d_use_Live_USB.
Most of distributions have ISO images which are bootable if you copy them directly to device (By directly I mean using dd). The other option is to install some bootloader on your USB device - this will, unlike first method, probably not wipe out all your data and partitions on device. Also, you can use some of those user friendly utilities like Unetbootin, but I myself have never had good experience with them.
I must warn you to proceed rather carefully, as you're always risking your data, even on your hard drives, if you happen to mistype device file. (e.g /dev/sda instead of /dev/sdc).
Good luck
Skyer
