Though my computer is only 4.5 years old, cringe, the weekly freezing, having 2GB of ram and being unable to keep too many things open at the same time made me decide to build a new rig.
My old computer, had the ZALMAN CNPS 9500 AM2 CPU heatsink/fan, bought at the time for $45.99. This massive heatsink with 3 pipes and 92mm copper blades is the thing to get if you want to OC. One issue was that it was so huge that you had to make sure that your motherboard and case would have enough room to fit this monster. And if you bought it, make sure you have a case with a window to show it off.
ZALMAN CNPS9900ALED, bought, ironically, for $35 after rebate.
Main difference? The 9900 will fit AM3 and also Intel, up to LGA 1156, not that I would buy an Intel cpu.
What else? It's bigger, it has a bigger dissipation area and depending on use, it may be slightly louder. Unlike the 9500, the 9900 does not come with a fan speed controller and adjusts the fan speed automatically. It also comes included with a resistor cable which changes operation from normal mode to quiet mode. If you don't care about the noise, keep the resistor off and you'll be getting as high as 2Krpm spin, but as high as 38dBA noise level, which is actually 10dBA more than its predecessor. Keep the resistor on and you'll be seeing 800~1,300rpm with a noise level of 18~28.5dBA.
One thing to remember about both these coolers, the blades are very, very thin and sharp and while they will not break, they will cut your skin if you're not careful.