For illustration purposes I'm offering you the block diagram of Athlon as well as Pentium III. Please refer to those diagrams to make following my explanations a bit easier.
AGU: Address Generation Unit
IEU: Integer Execution Unit
SSE: Intel's Streaming SIMD Extensions Execution Unit
BTB: Branch Target Buffer
BHB: Branch History Buffer
This is a die picture of the Pentium III die, which is not the same scale as the Athlon die-picture; the Athlon die is larger. The Pentium III (Katmai) is also manufactured in 0.25µ technology and it consists of 9.5 million transistors. Here you'll find some more facts .