Bootable usb , how?

By system repair what you meaning specifically?

If you have the cd image you can make it bootable on a usb drive using windows 7 usb tool.

If you don't have a cd image but it is a recovery console then have to make it bootable format

If you just want to make a bunch of programs bootable that is not really possible.
 
Step by step is rather long to type out, so I'll leave you with this link that does a great job of leading you through the steps. NOTE: Make sure you have a USB drive that is large enough, the free 2 gig sticks a company gave you with their logo is not going to be enough ;-)

http://www.intowindows.com/how-to-repair-windows-7-from-usb-flash-drive-repair-without-installation-dvd-disc/
 
Method 2 in the link has directions on how to do it after downloading the windows 7 iso. If needed, you can take a look through YUMI, but if you have a legit copy, you should be able to download the iso from Windows directly.