All that you can do at best is reduce it's shared video memory. This appears to be your machine's issue and it seems you've done great to get it down to 16MB.
As to the "goes wrong" issue. See if they updated the BIOS to allow you to set your new card as "Primary." If not, yet another limitation.
Ok well i have an emachines t3882 which came with Intel Extreme Graphics 2. So today i decided to put in my old Nvidia FX 5200 from my old pc to allow my pc to use its full ram and not have to share it with the internal card. SO everything is fine except that i cannot disable the Extreme Graphics 2. If i got into system, devices, and disable it, everything is fine until it turns on. When that does, the Extreme Graphics 2 is the main card and the screen resolution goes down and then i have to go through the whole process of making the Nivida card the main one and not extending windows into the Extreme Graphics 2 card. So how can i fix this. Is there any other way or is it that i just cannot disable it. Also if anything goes wrong, the video sorce automatically goes to the Extreme Graphics 2 card and shows nothing on the nivida card. On start up, while having the nvidia card as the main one, i cannot even see anything until the login screen comes on. It takes it that long to load for some reason. Is this normal? I would really like to have those extra 16mb of ram.