When just about any computer component (CPUs, RAM, motherboard chips etc.) is overclocked it generates more heat (especially when voltage is increased) and the buildup of heat is many times what limits substantial overclocking. It is also possible for two identical components to have very different overclocking ability. The only difference between the same CPUs that are sold at different clock speeds is that the faster ones are the parts that have been tested to run at higher clock speeds. The early versions of CPUs typically don't overclock as well as the CPUs manufactured at later dates. This is a result of the manufacturing process being continually tweaked to maximize production efficiency for the production run of that processor.
So, yes, it is important to have a good CPU cooler, fast RAM with heat sinks attached and especially a case that moves a lot of air through it. It is also important where fans are placed and their direction of flow. I use the method of expelling air at the top of the case while pulling air into the bottom of the case. Without good case airflow, substantial overclocking is nearly impossible to achieve because hard drives, video cards, media drives etc. all produce a lot of heat.
Most motherboard manufacturers have utilities for download that gives all kinds of information regarding motherboard functions. Most also have software to overclock CPU, RAM etc. but I prefer to log into BIOS and change settings there. It seems to be a more stable way to overclock, IMO. There are also many free utilities that do the same except for overclocking.
As for temperatures, I can only speak regarding socket 775 CPUs. Most of them will run stable with CPU temps under 58-60 degrees Celsius. I think cores in my Q8300 run at 48-52 degrees at 100% load.