using the internal 80g drive as though it were my computer's external hard drive

Hi.
I'm looking into the combined dvd burners with Tivo hard drives. Most
have 80gb or 120gb internal drives. Some say they have firewire
connectivity. My question is this:
Can I hook up one of these DVD recorders to my computer (an Apple) via
the firewire port, and use the DVD recorder's internal drive as though
it were an external drive for my computer? Similarly, could I use the
DVD burner as a firewire I/O device to my computer (so, for example,
use Toast or some such DVD burning application on my computer, then
have it write to the DVD recorder via the firewire port?).
Thanks much in advance for the assistance.