If you connect it to the same computer it is "paired" to for syncs, you can force the pass code off:

1. Connect your iPod Touch to iTunes
2. Press or Hold the power and home keys 10 seconds.
3. Screen goes black, now release the power button
4. Make sure you do not release the Home key until your iTunes says "We have detected an iPod Touch in recovery mode."
5. Restore the iPod

You will, of course lose any content which has not synced back to itunes from the iPod...

See also Apple's tech note on this.