to install Vista/2008 from usb.
Run CMD.EXE and type the following. Note: This set of commands assumes that the USB flash drive is addressed as "disk 1". you should double check that by doing a list of the disks (type "list disk") before cleaning it. If you have multiple hard drives, like an SDFlash drive or a Multibay drive, you could end up wiping your second drive using this command.
(This was a warning that Josh added to his post along with the following commands that I copied from him, so kudos to Josh)
1. diskpart
2. select disk 1
3. clean
4. create partition primary
5. select partition 1
6. active
7. format fs=fat32
8. assign
9. exit
now copy the contents from a mounted install disc or the real disk to the usb stick, reboot and boot from usb