Yep a core 2 duo is better than a pentium d.
Want proof look at these benchmarks:
Tom's Hardware Guide Processors: CPU Charts 2006
It doesnt actually have the lowest core 2 duo which is the e6300 but the e6400 is very similar. You may be wondering why your pentium d has a much higher clock speed than 1.86ghz and how the core 2 duo can be faster.
Well it beats it by far because the core 2 duo hasa completely different architecture. However both processors are dual core.