2800+ is equivelant to an intel 2.8GHz, but it's equivelant to an Intel Celeron and celerons are weak.
Besides the fact that they have low L2 cache, they simply cannot crunch numbers like their (in intels case P4's) or in the case of AMD their main line of AMD64 processors.
AMD's are better for gaming, but you need to get one of their 'power' CPU's meaning something like a 3000+ venice or something along those lines. Now, of course, that doesn't mean that a 3000+ is a "POWER HOUSE" processor by any means, because naturally you'd need to pay a little more to get something with a higher clock speed, but obviously it's common sense that higher clock speed = better. I guess the main Point I'm saying is, a 3000+ venice is only 1.8GHz but it would still beat out your 2GHz CPU......as the name implies a 3000+ venice even at 1.8GHz is approximately equivelant to a 3GHz intel P4 processor, whereas your Sempron, albeit having a higher clock than the venice, is not only approximately closer to 2.8GHz, but that 2.8GHz is a lot weaker than the 3GHz p4.....not just because of the clock speed, but because of it's overall structure as well.....meaning even if that intel celeron was up at 3GHz it still wouldn't compete one bit.
The semprons are the new generation of Durons, but if you don't know much about durons then that doesn't really explain anything.
Basically like I said though, it's the budget CPU's. It's not meant for heavy number crunching that's needed in games.