Heres a stumper for you (I know the diffrences but lets see if poster does, when he figures it out then he will get it)
The last Pentium 4 Chip to be released was the 3.8ghz Cedar Mill. 3.8 means that it ran at 3800 cycles per second, that was essentialy the fastest and best single core Pentium Chip.
Now look at conroe, their latest EXTREME edition runs at 2.66 ghz or 2660 cycles per second.
So obviously the conroe per second runs 1200 cycles less than the P4 but stumps the P4 performance by nearly 60%
as mentioned above a pentium will run 4 instructions per cycle, and the conroe will run 12 (I am simply quoting someone above I actualy think I remember reading that the Pentium4 did 6 instructions per cycle not 4.)
Essential the Idea is the same. Diffrent sockets diffrent CPUs diffrent ram compatibility ect ect.
Back in the day (hahaha back lets say 8 months ago) the major diffrence between the two major intell sockets 478 and 775 is that 775 supported Dual core processors and DDR2 Ram. Now 775 also supports Core 2 processors.