If your processor can keep up, you should get good framerates at 1680x1050 and below. It will be a major improvement over the integrated 6150 no matter which processor you have.
From the looks of it clutchc, I wold think he has some sort of pre-built system. DDR2 implies an older rig (not all the time though! look at mine!) and I would think that by the looks of that 6150SE I would say it might be an HP system. I have had 2 of them, they had dual core AMD chips (4600+ and 3800+) as well as 6150SE's.
For your computer, if you are not willing to upgrade the power supply, I would go with something like a Radeon 5670/6670. They are under $100 and are the best you can get for the money in terms of budget performance at the moment.
EDIT: I now feel stupid since I didn't see the title, it says Emachines on it.