Buy a used GTX 750 Ti on Ebay for $50 to $70, and continue with your current PSU.
Addendum: Upgrade from 3 GB to 8 GB RAM, assuming your OS is a 64 bit version (example below). I don't know if this specific memory is compatible because you didn't list your motherboard. It's for example purposes only. I must also state that this is the "most" that I would consider investing in that system. Next month your CPU will be 8 years old. I recommend that you consider building a new system in 2017. The GTX 750 TI can easily be transported to the new system, but this dated memory architecture cannot. Keep the boxes and packaging for both the GPU and RAM, so that resale in the future is easier...