12-23-2010, 08:56 AM
The version you have (the latest one actually) only has a tethered jailbreak, meaning, once you reboot your iPod Touch, you would have to redo it again. There is currently no untethered application used to jailbreak OS 4.2.1; rumors say this coming Christmas, the known hackers (Geohot, iPhone Dev Team, etc.) will release the awaited update. If you have other queries, feel free to ask.