If you can remember the email address associated with the AppleID along with whatever security questions are attached to the account you can reset the password.
On the App Store, accessed through the app on an iDevice, scroll down to the bottom and tap on the AppleID box. The ensuing pop-up box has an option for iForgot. Follow the onscreen prompts from there. You will end up on the Apple website and flitting between your email program and your browser. For that reason it might be easier to do it on a PC.
If you have upgraded the iPad to IOS7, things can get quite messy from now on as the AppleID of the user survives wiping the device as an anti-theft measure.