i am using autocad 2010 for that i am confused about between core2duo and quad core which one is better for autocad2010
Autocad 2010 only loads one core even if you have 200 of them, so you take no benefit from the number of cores alone (of course if you want to do other stuff while working, more cores mean less load on the core CAD is using). It also isn't Hyper-Threading-able, so you also won't get anything for HT-ready CPUs too.
You should look for better specifications per core instead, and as the Core2 Quad are generally better than Core2 Duo, get one of those.
The VGA plays some role into the workload only if you do wireframe 3d. Otherwise the onboard graphics will be enough and the CPU alone is the big deal. Also don't get fooled by Autodesk and Nvidia when they say you must get a Quadro. Quadros are a waste of money. Go for a Geforce instead.
Autocad products don't take any advantage of multiple cores. It may allow you to run multiple versions / different programs at once, but shouldn't degrade any performance of a running app. Not sure if clock speed is going to be a drawback though.