Not necessarily, the architecture of the Pentium D chips isn't nearly as efficient as the Core 2 Duos and wouldn't provide a major performance increase over the more recent Pentium 4s, albeit still an increase.
If you desire a vast improvement, save for a C2D.
Even if he wanted a C2D, odds are his board wouldn't be compatible with anything outside of the E4xxx series because of the Bus speed required by the higher models.
Even the E4xxx might require a BIOS update to work. There are no guarantees about any Core 2 working with any board made before August of last year (That would be about the time the Core 2s hit the market).
he said he wanted a Pentium D not a C2D. besides it is hard to be able to actually use all of the C2D power
http://www23.tomshardware.com/cpu.html?modelx=33&model1=444&model2=446&chart=171
clearly much higher than the P4
they are both the red bars. the higher the better
Even if he wanted a C2D, odds are his board wouldn't be compatible with anything outside of the E4xxx series because of the Bus speed required by the higher models.
Even the E4xxx might require a BIOS update to work. There are no guarantees about any Core 2 working with any board made before August of last year (That would be about the time the Core 2s hit the market).
the Pentium D almost doubles the P4's scoreHowever, comparing a P4 670 to a PD 805 yields a very little, unnoticeable difference. Ultimately it depends on the models he is looking at, which is what I was getting at.