Yes. You need better cooling. In Theory you can overclock processors to phenomenal speed increases provided you can cool them properly and provide them with a dependable current.
However, the cost of the increased cooling (in what you would have to purchase to be able to cool it) would outweigh the cost of a better processor. It's not a matter of hating on you because it is an older processor. It is a simple matter of economics.
Standard cooling won't handle the overclock. This means purchasing an aftermarket cooler design that is not something that would simply reduce temperatures by a few degrees. This would most likely mean a water cooling rig, a superior heat sink that is separated from the processor itself with heat pipes, a Peltier chip cooler, or even a combination of a few of these technologies. For example the Ultra Chilltec cooler combines a fan and heat sink, heat pipes, a Peltier chip, and a separate temperature controller to provide exceptional cooling over standard CPU coolers. Something like that would allow you to overclock your processor to the speed you are looking for. However, at $150, you are just throwing money away.
Because an AMD Sempron 2800+ runs at 2.0ghz, which is the speed you want. It operates on the 333mhz bus yours runs on (so you can almost certainly just swap it for yours), and you can buy one for $16. So... what you would spend to be able to overclock that processor would exceed what you would spend to replace that processor, to achieve the same speed. Plus, replacing the processor would be far more stable.
See... not hating on you or your choice. Just pointing out the economics of it.