Actually Pentium 4 processors that use the Prescott core are actually some of the best overclocking CPUs in the world, next to the Opteron and it's freakishly weird ability to overclock to insanely high frequencies.
The Prescott can handle temperatures of up to 80C before you really have to worry. With proper cooling inside the case, you can lower CPU enviorment temperatures dramatically. I did, although it took me $120 to do it, but, achievable nontheless. I suggest that you overclock your CPU by 10%, just take your CPU frequency, which you said is 2.4, so 2400 times .10 comes out to be roughly 240Mhz. So, overclock it by that much, see what happens. If the sh*t hits the fan, then reset the CMOS and resume activities as normal.
However! Be advised! Any overclocking you do, may or may not, cause damage to the CPU or any other componet to the computer (PC). Though highly unlikly, it has happened to people. Typically to those who fail to realise that cooling is VITAL. Raising the frequency to high can cause stress to the CPU and it's componets, but if you follow instructions carefully, you will avoide this and end up with a faster CPU, a faster FSB, faster RAM, and ultimately, a faster computer.
To actually tell the difference from a standard clocked CPU to an Overclocked CPU, you have to change the frequency by a considerable margin. I noticed a rather large improvement in my booting up times once my processor was overclocked by 500MHz. Although the system did have a tendency to become unstable, and by unstable I mean the main C:\Windows\System32\System.conf file went corrupt! And that, is bad...
But, just reset the OC to standard fequency and presto! you're good to go!
So, I suggest you OC that P4 to 2.6Ghz and see what happens. If the sh*t hits the fan, reset the CMOS, and you'll be back on track and reporting back to us in no time flat.