Run Windows from USB Disk

You cannot generally just boot an operating system on various hardware platforms - without going into too much detail this is for a whole host of reasons, mostly related to drivers/registry settings.

It is possible to boot certain distributions of linux "live" because they are designed to be that way - Windows 7 is not designed to be booted from removable storage on different machines and unless you get really lucky (both target machines are nearly identical hardware wise) it simply will not work, and there really is no way to make it work from your existing installation.

There are some ways to make a live bootable instance of Windows - but since your current installation was not built that way I am afraid you wont be able to make it boot via USB on your laptop - in fact you could potentially damage the installation by even trying to.

You can try this: http://www.intowindows.com/how-to-create-bootable-windows-7-vista-or-xp-usb-flashpen-drive-with-a-single-click-must-try/

However, your usb disk/key may or may not work. No warranty of any kind, as usual with free tools :-)