Panda, an antivirus software company, has a new free Panda USB Vaccine available for download that can disable the Windows Autorun feature for an entire PC or a particular USB drive.
The Autorun feature in Windows can make it easier to install software - and it can also be exploited by malware like the Conficker worm, which co-opts the feature to spread itself. I've previously written about the risk, and turning off Autorun can be a good idea for better computer security.
To download this small tool you'll have to first give Panda your e-mail address and opt-out of receiving marketing e-mails (unless you want them), but it's a quick download after that and doesn't require installation. When you run it, you can click a button to vaccinate your computer (disabling Autorun), and you can then click the button again to turn Autorun back on.
You can also connect a USB drive and choose to disable Autorun just for that drive. But note that it's a permanent step when done for a particular drive, and can't be reversed.