Onboard graphics card for my X3200 disabled

No need to break the seal on the box -- there's nothing to jumper or switch inside there anyway.

Some video card/motherboard combos will let you do this, others force you to choose one or the other, but here's how you find out.

Right-click on "My Computer" and select "manage" This will bring up Computer Management
On the left side of the Computer Management window, find Device Manager and click on it.
Now, on the right side, look for Display Adapters, and expand it. There should be an entry for your GT120 and hopefully another entry for your onboard video. Right-click the onboard video device, and one option should be "Enable"
If you don't see this option, it's because your onboard video can't work at the same time as the GT120.

Let me know how it goes! Rate me if it works, comment back if it doesn't work and I'll see what else I can do.