It will be able to run OB on max settings I believe. I have a 7900GS as well and it handles TF2 on max settings beautifully. I assume the processor is adequate.
That's a pretty nice set of specs for a laptop, I'm bemused as to why you only have 80gb of space though, my laptop has 160gb and worse specs (T7200, ATI mobility graphics)
When I bought the laptop, I had spent way more money than I had planned on the processor, RAM, and video card, so I had to go with the standard (price included) HDD. That's one piece that I plan on upgrading eventually.