you'll definitely need to beef up your computer's specification.
You're correct in thinking that you should upgrade your CPU (to the maximum speed that your motherboard will support) and the RAM. I would double the RAM, and if you can afford it after all that
click here to take a look at a clutch of recommended flat panel monitors. Buy the best monitor that your budget allows - CAD is one of the most demanding of computing tasks, and a good display is essential.