by doubledb » Thu Dec 10, 2009 6:42 pm
Yeah, you need to install a mobile installation patch on your iPod in order for this to work.
For 3.0 it was called "AppSync for OS 3.0"; for 2.x it was called "MIpatch 2.x"
I'm not sure what the title would be for 3.1.2, or if one even exists, but it's worth searching Cydia for.