Google around, there's a bunch of good walkthroughs on the topic. That's how I managed to get Vista drivers for a Radeon 9800 mobile card that hasn't been on the market for years.
There's absolutely nothing "proprietary" about most mobile graphics cards, they're all based on the same reference chip after all. The problem is that every laptop requires a different form factor, and thus a different production line, and thus a different PCI Vendor ID. The problem is that laptop manufacturers tend to neglect driver updates, notably after your laptop model becomes outmoded, and the generic graphics drivers only have desktop board vendor IDs listed.
Altering a driver can - on occasion - cause problems, but only if the driver you're messing with has dropped support for that particular chip.
[Edited by nephilim, 10/27/2009 5:25:14 PM]
The only thing nVidia really have going is hardware based PhysX support (they deliberately disabled hardware support for other graphics vendors, so no more using an ATi card as the primary 3D renderer with an nVidia part for PhysX).
And really, once the OpenCL version of Havok is available, I'm betting PhysX support falls by the wayside since OpenCL is supported by all major gaming graphics vendors (ATi, nVidia, and Intel).
The irony is that ATi used to be known for buggy drivers and since Vista (now on Win 7 Ultimate 64-bit), it's been just the opposite with nVidia drivers being far less stable and easy to work with.
[Edited by jack_deth, 10/31/2009 6:02:13 PM]