Open EasyBCD.
Click the “BCD Deployment” button.
Choose the UFD (USB Flash Drive) partition from the drop down. (MAKE SURE YOU HAVE TH RIGHT ONE!)
Click the “Install BCD” button.
This will add a BCD store to the UFD and make it bootable. It will ask if you want to load the newly created BCD file. Click Yes.
Now copy ISO or WIM files to the flash drive.
Click the “Add New Entry” button.
Click the appropriate tab for the type you are adding (ISO or WinPE).
Give it a name and browse to the ISO or WIM file.
Once you have an entry or two, click “Edit Boot Menu” to set the order, default timeout, etc.
Click “Save Settings” and close EasyBCD.
Your UFD should be bootable and contain the entries you added to the boot menu.

Note that EasyBCD only works on Win 7 / Vista.

http://neosmart.net/wiki/display/EBCD/Creating+a+Bootable+USB+Drive