XPS One 20-Need to upgrade video

I have an XPS ONE 20 [Svc tag: HD2NDD1] with the MXM7308-MG video card.

I'm trying to set this up as a gaming system for my son. I installed an SSD drive to help the speed and now the video is inadequate.It won't run Steam.

What are the upgrade options available for this system?

Anyone know what video cards would be compatible?

Would an nVidia NV9P-GS fit in the system?

I also understand that 4GB is the RAM limit, too, is this correct?

Thanks!