One of the new features of iTunes 8 makes it impossible to sync onto a jailbroken iPod Touch. It would sync with my jailbroken iPhone, but I have heard it is only for jailbroken iPod Touch. Downgrade back-2-iTunes 7.
Check Perhaps someone has a workaround on another forum. Otherwise you might have to go back to standard Touch Software. Apple has you Jailbrakers good now!