Your analogy of the Ferrari vs Nissan doesn't fly because a Nissan isn't a de-tuned Ferrari. However, most lower end CPUs in a series/family (based on the same CPU core) are just that - detuned versions of their high end cousins. The only difference is the default multiplier assigned to them.
Using the OP's Pentium E5400 as an example, it's based on the Wolfdale-3M core. From wikipedia: the Wolfdale-3M "is used in the Core 2 E7xxx series as well as the E5xxx/E6xxx Pentium Dual-Core and E3xxx Celeron processors". In other words, there are numerous CPUs that use the exact same core. In the Pentium-Wolfdale-E5xxx line, the only difference between the low end E5200 (2.5GHz) & the high end E5800 (3.2GHz) is the multiplier, otherwise they're identical. So in reality, overclocking a E5200 to 3.2GHz does not stress the CPU one bit.
"Why would Intel, AMD and so forth sell CPUs with more speed, if it's unnecessary, cause everyone can overclock the CPU"
Fortunately for AMD & Intel, most people think like you do - "overclocking is bad". Yes, everyone can overclock (provided they have a motherboard that allows it), but the majority don't because they're scared they may break something.
Are you using a USB or PS/2 keyboard? If it's USB, try switching to a PS/2. Install the Q8400, then clear CMOS. Boot the system & see if the PS/2 keyboard will allow you to access the BIOS & make the necessary changes.
message edited by riider