text: Core 2 Duo runs at slower clock speeds than Pentium-era chips, but is still more productive because it handles more calculations per clock cycle....Excellent for CAD drawings, Database hosting, Video encoding, etc. Much better than a single Pentium. \nWith that said, your question ask which is "faster" ...faster would refer to processing instructions quickly....which at first glance would appear the 2.66 pentium...but with a duo...the duo has it due to it's seperation of processors (can process simultaniously) (duo=2 processors in one chip) ...as for RAM...if your using the internet and MS Office apps...512 is enough! But if working with graphics, videos, databases or CAD you will certainly need to increase the RAM in the 512 PC. and set the paging file from 524-1024 this will use your physical RAM first and the other 512 on the hard drive as needed. \nI would go with the DUO and boost the RAM if needed....remember it's far cheaper to upgrade RAM.