I'm not sure on this, so I hope someone will come in and correct me if I'm not, but I just installed OZ yesterday, and it looks like you'd want to setup a destination in the packet manager. Open that up, go to (may not be the exact wording) Action --> Configuration, click on the Destination tab, and create a new destination. Label it whatever you want (sd, cf, etc) and make it /mnt/card or /mnt/cf and I think that'll do it. I'm not sure if you'll need to "select" the destination before you install or if it'll ask when you install, but give that a shot.