Just a couple of cautionary notes.
First, the OP's computer is an older (probably 4-5 years) model, for which I have been unable to find certain specs. In this case, it's the power supply unit (PSU). I'm going to guess here, and peg its output at a nominal 300W. Because of this, the OP should avoid any video card that 1.) requires an auxiliary internal power connection (cannot be powered solely by the PCIe x16 expansion slot) and 2.) has a manufacturer's minimum wattage requirement greater than 400W.
The nVidia GT210 card he listed should be avoided, not because it's necessarily a "bad" card. But it's far less capable than either of the other two cards he was looking at. (For nVidia cards, the second digit in the model number shows the video capability of the card. Higher numbers are better. ATI cards are similar in that respect, the higher the number, the "better" the card is in rendering graphics.)
Unfortunately, the card that Mega listed is likely to be too power-hungry for the OP's PSU to handle, and probably requires an aux power connection.
And yes, it's possible to upgrade the existing PSU with a newer and higher-output model, but that's an extra expense that may not be necessary. After all, we're not talking about using this machine for playing the "latest and greatest" first-person shooter game. Improving it to better handle RoM's graphics is the goal.