how do you over-ride a forgotten passcode?

Passcode to what? The screen lock on an iPod touch? If that's what you mean, restore the iPod from the computer to which the iPod is synced. For information and instructions, see:

http://support.apple.com/kb/ht1212

If that will not work, you'll need to put the iPod into Recovery Mode and then try the Restore again:

http://support.apple.com/kb/ht1808

If that still doesn't work, as a last resort try DFU mode:

http://www.iclarified.com/entry/index.php?enid=1034

Regards.