When I pop my verbatim dvd-rw disc in with the finder, it asks me what I want to do with it. In that case, prepare it for use (data, for example). It then acts like a cd....drag and drop onto it, then when I ejected it, it wrote the 4.4gigs.
I put it back in, and it showed up in the Get Info, as a DVD-RW disc. To format it, I had to use toast (5.1.4...which let me completely use it...however I wanted...format, music, whatever). But in toast, if I formated it, ejected it, left toast and put it back in, while in the finder, the first part would happen again (asks me what I want to do, etc..).
Maybe it's cause you have the new powerbook....I dunno. Since it's pretty new, just call up apple...you have 90 days tech support, without applecare! hehe