With VoiceOver 'on' you need to tap a field and it should then get a box around it and then double-tap to activate/type it - so to type one of your passcode digits tap it and then double-tap it to type it.
Once you've typed your passcode you can use then either turn VoiceOver 'off' directly on the iPad (you need to use the tap-to-select and then double-tap to activate/type process and 3 fingered scrolling) via Settings > General > Accessibility > VoiceOver 'off', or you can do it by connecting to your computer's iTunes : http://support.apple.com/kb/HT4064
Turn off VoiceOver
1. Press the Home button
2. Tap Settings.
3. Then double-tap Settings.
4. Tap General.
5. Then double-tap General.
6. Use three fingers on the screen to scroll to Accessibility
7. Tap Accessibility.
8. Then double-tap Accessibility
9. Tap VoiceOver
10. Then double-tap VoiceOver.
11. Tap "On" next to VoiceOver
12. Then double-tap "On" to turn it off.