Atom PE Express-> USB
*Update* You can download AtomPE to USB Program AtomPE - USB Beta
Download Atom PE Express .iso from here -> Download Atom PE Express
Download our Grub4dos files from here -> Download grubinst-USB-drive.zip
When we have the files that we want, the next step it ts extract our .iso to a folder.
This will take some time as its 3 GB of data...
While the .iso is decompressing....
We can format our USB Drive, simply right click on the drive and chose "format" the defult file system type should be "NTFS"
When our image has been decompressd and our USB Drive is ready. simply copy the contents of the .iso to the root of the USB drive.
Run Grub Installer
When You have the "grubinst-USB-drive" extraced to a folder you will find the program inside call "grubinst_gui.exe" if your using windows vista or 7 make sure to right-click and "Run as Administrator"
When the program opens make sure to select the flash drive as the disk you wish to use.
!!!Warning!!!
It is possible to damage your curent os boot loader with this program!
Make sure that you have your flash drive selectED!
Click the Part List Refreshbutton, then the dropdown box, and finally select the Wholedisk (MBR)
Check the "Don't search floppy option",
Click the Install button to install Grub4DOS to the MBR of the flashdrive.
A Command window should pop-up. Just hit enter
Now just Copy the "grldr" file in the folder "Copy-to-root" to the root of your flash drive and reboot!
Source
Making Changes
Since we have installed Grub4dos as our main bootloader on our flash drive here a guide that will make it easy to make changes to the bootloader so that you can add or remove .iso to your flash drive.
Grub boot loader guide.