I installed a new hard drive in my husbands computer and was going to install windows 7.   I ended up formating the drive from the dos prompt (such as it is) but when I tried to transfer the system FILES it doesn't recognize the command.  When I try to do the installation of windows 7 it fails because of missing system files. You need to BOOT to the Windows DVD to install. Set the DVD drive as the first item in the bios boot order.I did.  aftert he failure the first time I got out to the dos prompt and ran the format command the drive was formatted but the /s didn't work.  I figured that was ok after the format I would just transfer the sys to it.  That didn't work.  I tried again to boot and install windows 7 and it failed after a fashion.
 
You don't need to use DOS commands at all to install Windows 7.

In fact, neither 2000, XP, Vista, nor 7 require DOS commands to install.

Don't use DOS at all.  Just:

1) Put the Windows 7 DVD in the DVD drive (it is a DVD drive, right?)
2) Go into your BIOS to change the boot order (usually by pressing "Delete," "F1," or "F2.")  Alternatively, some PCs/motherboards have the OPTION to select the drive you want to boot from without going into the BIOS options.  Usually, that key is F12, but it may not be that.  Pay attention to what the initial screens tell you and see if there's an option to go into "Setup" or "Boot Order."
3) If you did #2 right, you should see "Press any key to boot from CD or DVD..." (sometimes this won't show up if the bootloader doesn't detect a formatted hard drive--it'll skip this altogether).  If you see the prompt, press something, and the process should start from there.There is no dos prompt. Boot to the Windows CD and shortly after the install process starts you will be give the option to format before installing. WHATEVER you're doing, you are NOT booting to the Windows CD