I showed someone this a few days ago and they suggested I blog on the simplicity of using powerISO. The easy way to create a bootable USB drive is to download powerISO from http://sharepointadam.com/2010/11/18/import-user-profile-photos-from-active-directory-into-sharepoint-2010/ you need version 4.8 or newer version 5 is the current version
After installing powerISO and rebooting your system click on the powerISO icon and you will see a GUI like the following.
Click Tools then click Create Bootable USB
Next choose the Source Image File and the Destination USB Drive and click Start
When finished just click OK
Of course you can always do it the old way
Or use the Windows 7 USB/DVD download tool http://www.microsoftstore.com/store/msstore/html/pbPage.Help_Win7_usbdvd_dwnTool