Touch or tap the field that you want to use/select and it should get a box around it ; then double-tap that field to activate/type it. Once you've entered your password you can do the same (i.e. touch to select, double-tap to activate) to gradually get into Settings > General > Accessibility > VoiceOver and turn it off.
So to enter your passcode you first need to tap the 'slide to unlock' button to highlight it (it should get a box around it), then double-tap it to unlock it. Then for your passcode tap the digit that you want and it should get a box around it; then double-tap that digit to type it; and similar for the other three digits in your passcode. And then turn off VoiceOver.
The manual (http://support.apple.com/manuals/#ipad) also says that you should be able to switch voice-over off by connecting to your computer's iTunes :
Turn VoiceOver on or off in iTunes: Select iPad in the iTunes sidebar. In the Options section of the Summary pane, click Configure Universal Access. Select VoiceOver, then click OK.
So select Configure Universal Access at the bottom of the Summary tab and set Seeing to Neither