Don't do it.. with 3.1.2 the ONLY jailbreak that works is blackra1n and thats a dirty tethered jailbreak (on late 2nd gen ipods, all 3rd gen ipods and iphone 3GS - other earlier models should be untethered by now on RC version) meaning if you reset your ipod or it crashed it wont restart until you connect it back to the computer and blackra1n.. Also once its jailbroken you can ONLY add jailbroken apps as its altered the boot code and NOT recognised as a valid ipod so wont load NEW apps and NEW protected items (apps or DRM music). YOU CAN load itunes Plus music and stuff you import from CD or MP3 or AAC files etc...
go to the site you got the jailbreak from for their links for apps if thats your thing.
NEVER JAILBREAK its NOT worth the effort or the RISK. you know that 75% of jailbreaks fail! either immediately or after a few restarts - if your'e lucky a restore in itunes will fix it otherwise its bricked and dead.
if you have a PC and its doesn't restore get a friend who has a mac to try as sometimes that can work!
This type of question is why I tell people NEVER to jailbreak
also jailbreaking removes security making it open to trojans (see news) and any files you have on it by say air-sharing app etc will be hackable too! as jailbroken iphone is as secure as your wallet being left in the open!
NEVER JAILBREAK! It causes so many problems and yet adds nearly nothing! here is only 25% chance of success with 50% chance of killing it. and any attempt voids any warranty you have! Once you have jailbroken an ipod you are then stuck with jailbreak apps as you can no longer add official Apps (or protected music) to the ipod as itunes will NOT recognise it as an official ipod. also updating an Jailbroken phone is very likely to kill the unit best option is to remove jailbreak by restoring it to pre jailbreak state using the backed up firmware then updating and installing the jailbreak later (if you must)
the 2.2 or 3.1 software from apple is stable and works well and lets you add hundreds of apps (many free) from the itunes App Store, many with features available in jailbroken items.
Jail breaking became redundant when the 2.0 software was released as it add almost nothing useful to the ipods abilities (other than the ability to browse its file structure which also makes it less secure).
Jail breaking also voids the warranty and does cause many issues from files vanishing, memory leaks and loss, rebooting and even failing to boot.
Jailbroken ipods cause so many problems (just search on here for them). It alters the boot code so its not really an ipod at all.
Best option is to remove the jailbreak by restoring the ipod on your computer but NOT connected to internet and make sure you have a full power
USB2 port as low power laptop ports can cause the restore to fail and kill the ipod. So... with itunes running reset your ipod (its the home and power key until screen goes blank with dark apple logo). then as soon as the screen lights up connect it to computer.