Logging to your PC with an USB stick is both useful and safe – not only aren't you limited by memorising passwords, but also you can prevent from accessing the computer anybody who you wouldn't like to use it. How to create a key like that in Windows 7 without installing additional software?
Only a few “chosen” people know that Windows enables you to create a security key that can be stored on...a floppy disk. But who uses them anymore?! Luckily for you, it is possible to save the key on a pendrive... with just a bit of effort.
1. Change the letter of your removable storage device
Since it was designed for floppy disks, the tool does not work with pendrives... until you change the letter of your USB key. To do it, get into Control Panel and choose Administrative Tools, then Computer Managament. While you're in there, you can manage your volumes by clicking on Disks Management. Right-click on your USB's icon and from the context menu pick “Change the letter and path...” option. Go for “Change” and pick “A” from the list of possible disk letters.
2. Creating a key on an USB
Now launch Run... and type in a command syskey that allows you to access Securing the Windows Accounts Database menu. Choose “Update”, and later on go for “Store Startup Key on a Floppy Disk”. Confirm with an OK.
Syskey.key should appear on your pendrive. Remember not to remove it, as Windows won't boot without this file and you would have to format your PC to access it!