If you compare the Intel® Pentium® D Processor 945 with the Intel® Core™2 Duo Processor E6600 the major differences that you'd find are the front bus speed being 800Mhz on Intel® Pentium® D Processor 945 while it is 1066Mhz on Intel® Core™2 Duo Processor E6600..
Also the features VT± Intel Technology.
Check the comparision charts and Intel site and Toms Hardware for benchmarks.
*indigo.intel.com/compare_cpu/showchart.aspx?mmID=884354,883951&familyID=1&culture=en-US
*www23.tomshardware.com/cpu.html?modelx=33&model1=432&model2=437&chart=169
I think the price difference between these 2 processors should be close to 45%.