I am trying to install Windows 7 Professional from USB 3.0 flashdrive, on a Thinkpad T61. The problem is, Thinkpads BIOS will not detect the flash drive as bootable medium, and won't allow to boot from it.
What I did:
Enabled USB BIOS Support in BIOS (it was on by default)
In startup menu, added USB HDD to boot order (it has '-' sign in front of it)
Created Windows 7 install media with UNetbootin, WinUSB (linux tool) dd and Grub4DOS.
As you can tell, currently, I only have access to Linux machine to make the flashdrive.
The T61 BIOS shows '-USB HDD' in boot order menu. The '-' sign suggests that the plugged flash drive is currently not bootable. The same flashdrive (with the same Windows image on it) is booting without any problems on a Dell D430 and Lenovo Y550. Also, Ubuntu 12.04 install USB created with Unetbootin shows as bootable ('+' sign in BIOS boot order menu) and boots from the F12 boot menu.
thinkwiki.org says that some Thinkpad BIOSes do not use MBR on flashdrives. It suggests using Extended-IPL boot loader, but the provided links are broken and there seems to be no mirrors.