Sometimes you need the UDID for your iPad, iPod, or iPhone and you don’t have the device. Or you do have the device but it’s b0rked, like from installing development iOS and forgetting to add the device to your account. And you’ve got a Windows desktop, so all the Mac instructions out there don’t help a ton.
It’s simple. Start->Run, then:
The folders there are named according to your device UDIDs. You can probably use the folder dates & times to figure out which is which, or if you need to get more detailed open Info.plist or Manifest.plist and look at the applications that were installed.
If you need your device’s serial number check this post.