I assume you're asking 'What's the difference between Pentium D and Core 2 Duo?'
First it depends on the specific CPU, but here's a generalized comparison.
The advantages to the Core 2 Duo:
FSB Speed 1066MHz vs 533MHz
Lithography 65 nm vs 90nm
Intel® Virtualization Technology (VT-x)
Enhanced Intel SpeedStep® Technology
Thermal Monitoring Technologies
Pentium D - http://en.wikipedia.org/wiki/List_of_Intel_Pentium_D_mi...
800(4×200) MHz front side bus
LGA 775 (Socket T)
Smithfield – 90 nm process technology (2.66–3.2 GHz)
Introduced May 26, 2005
2.66–3.2 GHz (model numbers 805–840)
Number of Transistors 230 million
1 MB × 2 (non-shared, 2 MB total) L2 cache
Cache coherency between cores requires communication over the FSB
Performance increase of 60% over similarly clocked Prescott
2.66 GHz (533 MHz FSB) Pentium D 805 introduced December 2005
Intel Core 2 - http://en.wikipedia.org/wiki/Intel_Core_2
Conroe – 65 nm process technology
Desktop CPU (SMP support restricted to 2 CPUs)
Two cores on one die
Introduced July 27, 2006
SSSE3 SIMD instructions
Number of Transistors: 291 Million
64 KB of L1 cache per core (32+32 KB 8-way)
Intel VT-x, multiple OS support
TXT, enhanced security hardware extensions
Execute Disable Bit
EIST (Enhanced Intel SpeedStep Technology)
iAMT2 (Intel Active Management Technology), remotely manage computers
I'm not sure what your talking about specifically.
Generally, Intel uses the "Pentium" brand for their worse processors in each generation. Currently, you can buy Pentium processors, but they are all worse than the intel core i3, which is worse than the core i5, etc.