From all the articles I read, I looks like a XPS Gen. 2 loaded with the 7800. Other than that there isn't a difference between the XPS M170 and the XPS Gen. 2. The GeForce Go 7800 will boost your 3DMark05 scores to the 6000 range and increase gaming performance but that is about it. The current generation games look fine on the 6800 Ultra and this graphics card should be able to handle a couple of generations of games, maybe up to the new Unreal Engine in which the 7800 will even struggle with. It doesn't look like the XPS M170 will include dual-core processors, I don't know why Dell would include the Pentium D (if they did) as it would be a step back from the steps they took with the XPS Gen. 2. The dual-core Pentium M is coming out soon but isn't slated for release until late 2005/early 2006. Since we don't know the release of the XPS M170, maybe Dell will be including the dual-core Pentium M processor.
Until Dell officially releases information, it is all just speculation about the XPS M170 except that it will include a variant of the GeForce Go 7800 gpu.