|If you are using an add in PCIe graphics card then you don't need to do anything. |
Going back to your original post you stated you are reading the results of nvidia control panel. I am not familiar with that utility. That said, I suspect that all you are seeing is the specs on the on board graphics chip.
The term dedicated memory can be confusing. When memory is part of the graphics card, as it is with the 9400GT it is dedicated RAM. However, your on board graphics chip can allocate up to 129MB of system memory to the exclusive use of the graphics. That 128MB is said to be dedicated.
If you added system memory (RAM) at the same time as you installed the 9400GT you may have done something wrong.
When you boot the computer do the start up screens indicate you have 4GB of installed RAM running in dual channel?
You didn't answer my question about where the monitor is connected. Do you have the monitor connected to the 9400GT?
Go to Device Manager and see what is listed for display adapters. Post back the results.
Did you install the latest drivers for the 9400GT in Windows 7?