Hi, The E2140 is an excellent overclocking chip, it very easily goes up to 2.8-3 GHz if your motherboard allows for overclocking, if you are unfamiliar with overclocking read a few tutorials off the net before attempting.
You did not mention the wattage of your PSU but I always assume around 300-350 you can check the wattage by removing the side panel and reading the chart on the side of the PSU, if you want a quick graphic upgrade check out this:
HIS H675F1GD Radeon HD 6750 1GB $99 http://www.newegg.com/Product/Product.aspx?Item=N82E16814161379
But I would recommend a good $50 PSU in the 450 watt range for the overclock and the GPU.
Thermaltake TR2 W0070RUC 430W ($34 after rebate) http://www.newegg.com/Product/Product.aspx?Item=N82E16817153023
You do not need a new computer, you just need to tweak the hardware you have... plus a GPU...