You should have upgraded to OS 3.0 and THEN jailbroken your Ipod.
It works this way, you jailbreak your ipod's firmware depending on your version of the firmware. Each version has a seperate hack. For e.g. the jailbreak for OS 2.0 will NOT work for firmware 2.2.1. Basically jailbreak install a 'cracked' version of the firmware. So you don't have a genuine copy of the OS so to speak.
As far as I know, you can only BUY the original firmware for $10 I think, through Itunes. But I might be wrong. I didn't look into it coz I wasn't eager to upgrade. An OS upgrade is not something that can be done on the fly within Installous or Cydia. You won't ever find it there.