1. I have that exact same processor. Two cores is roughly equal to having two processors in one container. They are very useful when running some applications that can really take advantage of them working in tandem: video compression, .mp3 encoding, some games, graphics work, CAD, etc.
2. Some Athlon X2 processors are well-known to have very poor temperature monitoring capability. AMD is well aware of it, but did nothing to fix it. The Brisbane core models are especially bad... I have one. When I installed SpeedFan, I was getting 60°C temps at idle, and 75°C at full 100% load (Folding@Home). I adjusted SpeedFan to read perhaps 2° or 3°C over room temps at idle because I have a direct duct to the outside of the case to pull in room air. Now, when my room is 27°C, my CPU reads 30°C at idle, and 45°C at full load.
Tom