If you've forgotten the passcode to unlock the iPad then you will need to connect it to the computer that you normally sync to and you should then be able to reset the iPad and restore/re-sync your content to it (http://support.apple.com/kb/HT1212) - you may need to put the iPad into recovery mode in order to be able to reset it : http://support.apple.com/kb/ht1808
If you do it via a different computer then :
If you restore on a different computer that was never synced with the device, you will be able to unlock the device for use and remove the passcode, but your data will not be present.
If you forgot (or don't know) your passcode, restore the device from backup on the last computer it was synced with when the passcode was turned on... this will remove the passcode. If you do not have access to the last computer it was synced with, you will have to force it into recovery mode & restore as a new device.