If you do not have a Windows 7 installation DVD, you can download a legal copy with SP1 integrated from here:
http://www.mydigitallife.info/official-windows-7-sp1-iso-from-digital-river/"]Official Windows 7 SP1 ISO from Digital River[/url].
Make sure you get the same version you have, Home Premium, Pro or Ultimate and 32 or 64 bit. Note that Basic or Starter is not available.
I recommend using
http://www.imgburn.com/"]ImgBurn[/url] at 4X speed (or the slowest available) to create the DVD from the downloaded .iso file.
You can do this on any computer capable of burning a DVD.
For techies or folks who work on computers:
http://www.mydigitallife.info/create-windows-7-universal-iso-with-all-editions-selection-on-install-with-ei-cfg-removal-utility/"]Create Windows 7 Universal ISO With All Editions Selection On Install with ei.cfg Removal Utility[/url].
This will fit on a 6GB flash drive or can be burned to a DVD.