You're really searching for a fruitless end. Overclocking is so 1990's and everyone here has already said you won't benefit from it and in fact would likely take a step backwards. Personally I don't know if it is even possible on Mac's. I've never looked into it as I haven't overclocked anything since way back with Windows 98.
What overclocking does is raise the frequency of the CPU which in turn consumes more power (electricity) and thus creates more heat. Heat can be a big problem for the rendering stuff you're talking about, as too much heat can actually slow the computer down if not stop it completely. Then there is the stability factor, OS's don't always respond too well when the clock speed and/or multiplier and voltage are changed.
Plus laptops by design have poor ventilation and the manufacturers usually design just enough ventilation to make it work properly as designed. If you up the CPU speed and create more heat, it will be that much harder for the enclosure and fans to dissipate that heat.
If you do find a way to do it, you'll be disappointed in the performance. I know you said you can't afford a new computer, but realistically that is the only way to overcome the problems you describe. Otherwise, keep using the same one and just have some patience.
