If you connect it to the same computer it is "paired" to for syncs, you can force the pass code off:
- Connect your iPod Touch to iTunes
- Press or Hold the power and home keys 10 seconds.
- Screen goes black, now release the power button
- Make sure you do not release the Home key until your iTunes says "We have detected an iPod Touch in recovery mode."
- 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.