Some of us have bought U3 drives and have noticed that they load software with out your permission. While this can be great if it you are wanting to get to your data, it is bad if you are letting someone else put the usb drive in or even one you found and want to check out. Bad things can be put on a USB U3 drive and a CD drive as well. Turning off autoplay is a good way to help control unwanted software from loading through the autoplay process.
I found some ways to turn off autoplay in windows. for XP and Vista there is a policy that can be set to turn off autoplay for the CD drive only or all drives.
Run gpedit.msc from the run line or a cmd prompt. Go to computer configuration – Administrative Templates – System – Turn off autoplay. When you enable the setting you can block the CD drives or all drives.
There is also a registry entry that can be made to block individual drives or all drives. This is described at this site. http://www.pctools.com/guides/registry/detail/156/