Here is a list of MXM compatible notebooks:
If it's not on that list, it means it's proprietary. Generally, if your notebook uses integrated graphics, you won't even be able to find a proprietary card. If it has dedicated graphics already and you want to upgrade, you *might* be able to find a card, but only if the manufacturer offers it as an upgrade. Even then, you would have to buy it used, or pay a ridiculous amount of money to have a new one ordered.
I'm pretty sure that HP Pavilions with discrete graphics have GPUs and VRAM soldered onto the motherboard. So you would have to replace the entire motherboard with another motherboard that has a better graphics card. As far as I'm aware, the best you can get on a DV9000 is a GeForce 7600.