RE: Upgrading a Dell Inspiron N5110
You can do this, but to upgrade from integrated to nVidia, you'll need not just the mainboard, but also:
A new heatsink assembly (the existing one won't fit the nVidia board) and
If you have a 65 W power supply now, it'll need to be replaced with a 90W or higher capacity one (65W is fine for Intel video but will not power the nVidia board).
Bear in mind that complete, used N5110 systems go for $150-300 on EBay -- in other words, you may wind up paying more in parts than you would buying a used system. There are also easier systems to work on (this one is probably the least service-friendly system Dell has sold).