Socket 754, so no dual channel. Slick_Tech15's advice is good advice.
The CoolerMaster PSU he recommended will be plenty of power for your system.
After you get all of that done, you may want to look into getting a full-fledged CPU. The Sempron you have is basically a gutted version (with 1/4 the onboard cache). You can get an OEM Athlon 3400+ Newcastle for $147, or $156 with different stepping.
My Rig: SABLE
Antec 300 Illusion / Antec EarthWatts EA650 650W / EVGA GTX 760 2GB
AMD FX 8320 x8 Black Edition / Gelid Tranquillo / MSI 970A-G43
Sandisk Ultra Plus 128GB / Samsung 840 120GB / WD Black 750GB / WD Green 1TB / WD Red 3TB
G.SKILL Ripjaws 2x2GB DDR3 1600 - Crucial Ballistix Tracer 2x2GB DDR3 1600
Win7 Ult 64-bit - Func MS3 Mouse - CM Storm QuickFire Rapid Mech Keyboard
R.I.P. Danny L. Trotter
... 14 Nov 1945 - 4 Sept 2009