Windows Vista and Windows 7 can be installed via a bootable USB drive as well.And the installation would be much easier and faster than installation via DVD.Windows Server 2008 & Windows Server 2008 R2 also can be installed via USB drive except installation of Windows 7 & Windows Vista .Initially Windows Vista/7 DVD or installation source (setup backup files stored on local hard disk) & a 4GB USB 2.0 Storage device would be required.You can follow the steps to install Windows Vista/7 from USB Drive.

1. Plug your USB storage device and run CMD and execute the following commands one after another.

• Diskpart
  Run Disk partition utility
• List disk
  To get disk index that is used to perform disk partitioning.
• Select disk 1
  Selects disk to perform disk partitioning.
• Clean
  Flush your existing all USB drive’s partitions.
• Create partition primary
  Creates a partition as primary partition.
• Format recommended
  Format your USB drive with recommended parameters. (No need to worry about file system format)
• Active
  Set the partition as active to hold bootmgr.
• Exit
  To quit Diskpart utility

2. After executing the above commands simply copy all Windows Vista/7 files from DVD/Backup storage to USB storage device.

3. Change boot settings from BIOS and set it to boot with your USB drive, you can install Windows Vista/7 via bootable USB storage device.That is it .

Note:For boot problems try Fixing your USB Storage drive with the command  I:\Boot\Bootsect.exe /NT60 I: where I: is the drive letter of USB storage device

Tx to Ramesh @ WindowsValley.com for sharing this trick.