A core 2 duo at 2.4ghz is twice the computer a P4 at 3.2ghz is.
The Core 2 duo name means it has 2 processor cores instead of just one. So you don't have a 2.4ghz cpu, you have TWO, so if the program is smart enough to use both cores, you actually have a 4.8ghz. But even that isn't true, because the way the cpu works is also more refined, so what you have to look for is the performance name. For example, a core 2 duo at 2.4 is likely an e6600. 6600 is the indicated performance. So, in that case, even two P4s at 3.2, aren't as good as a single 6600.
Have fun with the smooth running MAME now. ;-)
All work and no play makes me..., well, you know the rest.