They both use the same type of RAM.
The architecture of processors is different.
AMDs have shorter instrution pipeline when compared to that of INTEL. Hence they perform better and run hotter even though they hav lesser clock speeds.
AMD has L1 cache of 128K compared to 16K of Pentium.
From the user's point of view--
Needs high multitasking capability--Go for P4
Requires a very good performing processor----AMD
Requires a good processor for gaming--AMD
Requires a processor to handle heavy image editing stuff or wit a very high Content Creation index,Price no bar----P4
Requires a processor which can outperform the intel at the same price----AMD
A Processor which is more futureproof--AMD 64 series