Do you have the correct settings in your control panel, it is hd2/60 for 1080 ntsc and hd1/60 for 720 ntsc , it is all described in the ref manuals hd section.
Previewing of an hd timeline is not possible through firewire, only sd is possible.
Workflows for how to get your project to a hd tape is well described in the ref manual, a new file will first be created and after that, the exporting begins.