The (Original) Pentium 4 Uses a 100Mhz Bus, Quad pumped (aka 4 accesses per cycle) i.e. giving an effective 400Mhz Bus.
The New 133Mhz Based Pentium 4 has an effective bus speed of 533Mhz (4x133)
AMD Athlons (T-Bird Core) and Durons use a DDR (Double Data Rate) 100Mhz Bus. i.e 200Mhz
New Athlons i.e. XP use a 133 DDR Bus i.e. 266Mhz
Future Athlons may use a 166Mhz DDR Bus i.e. 333Mhz