I would really go with the Core 2 Duo, because even though the Pentium D looks like it has a better CPU speed, the truth is that C2D is 1. Dual Core, and 2. Easily overclocked.
Take into concideration that Pentium D's are an older generation of CPU's and they are far less efficient.
I would strongly recommend ANY C2D over a Pentium D, Athlon, AM2.