43 degrees celcius idle on amd sempron

43°C is fine, especially considering you've got the stock cooler. Max temp for this class is ~65°C. The sempron 3800+ is a 62W CPU. My Phenom II X4 945 is a 125W CPU. Using Artic Silver 5 and a Titan Fenrir CPU cooler, my idle temp is ~42°C. So, you see, your temp is well within tolerance.

Should you choose to OC, you should consider getting an after market cooler, or even better, upgrade your CPU/mobo, get a Black Edition, and an after market cooler.