You will definitely need a bigger PSU to run a standalone graphics card of any quality. If you're in the U.S., get this Antec High-Current Gamer unit, probably the best deal you'll find on a well-built power supply right now:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371059
In the bigger picture sense, there are other issues:
- Even after this upgrade, you will be severely CPU-limited in modern games by that old Wolfdale dual-core. If you have the budget for it, you will want to replace the CPU and motherboard. If you are going to lack the money for that, at least try to pick up a Core 2 Quad for $50 or so to help ease the bottleneck somewhat.
- Older motherboards sometimes do not support PCIe x16 3.0 cards without a BIOS update. Your odd-wattage, off-brand power supply, 6 GB of RAM and integrated graphics makes me think this is a prebuilt system that was upgraded from 2GB to 6GB of RAM, which helped things by alleviating a bottleneck, and now you're looking to do more. Prebuilt systems are notorious for using motherboards that do not support new things and never get BIOS updates. It may not even support a C2Q processor either. Look into that before doing anything.
Overall, you may get a small boost from the GPU and power supply, but is it worth $100+? Not really. The best option is to start from scratch, and second-best option is to do the quad-core, PSU, GPU upgrade with an eye toward getting a GPU good enoguh to bring into a new system about a year from now.