While out there are many utilities or tools for one to create a bootable USB drive for Windows 7 installation, the DiskPart program comes with Windows XP or above can also be used to get this job done without extra cost.
How to create bootable USB drive of Windows 7 installer via diskpart command.
You should able to follow these steps, to create a bootable Windows 7 USB flash drive, in Windows XP or higher. In brief, the key point is using diskpart to set a partition to active (bootable) and then copy the Windows 7 DVD content into this active partition.
1) Connect a USB flash drive (min. 4GB for Windows 7 Ultimate 64-bit).
2) Open Command Prompt window and execute diskpart. In Windows Vista / Windows 7, you need to run Command Prompt with elevated privilege.
3) At DiskPart prompt, type list disk to display a list of mounted disk drive detected by Windows. In the list, you should be able to recognize the USB flash drive connected to Windows, by looking at the Size column. (In my screenshot, this is disk 2).
4) So, execute select disk 2 and then run list partition to display the partition table of the selected disk 2 (i.e. the connected USB flash drive).
Having said that, it’s possible to create multiple partitions on a big USB flash drive (16/32GB or bigger), and uses one of the partition that is fit for the Windows 7 installation files. As mentioned earlier, 4GB is recommending for Windows 7 Ultimate 64-bit.
5) Execute select partition 1, suppose I would like to choose this partition to work on. Indeed, that is the only partition on the USB flash drive.
6) Now, execute active to set the selected partition as active partition (i.e. bootable partition). By then, the list partition report will display an asterisk mark in front of the “active” partition record.
7) Exit from DiskPart program and proceed to use robocopy to duplicate Windows 7 DVD contents to the “active” partition of USB flash drive. For example:
robocopy D:\ E:\ /MIR /V /FP /LOG:C:\Win7.log /TEE
Where D: is the DVD drive containing the Windows 7 DVD; E: is the active partition of USB flash drive; /MIR is to mirror whatever inside the source to the destination; the rest of option switches used are for logging purpose.
Once the robocopy completes successfully, there you will have a bootable USB flash drive for Windows 7 installation :-)