You haven't mention anything about the size and power of the RAM, data transfer rate of the SATA cables or hard-drive you're using. Though you got to keep in mind that you probably have an older operating system on your old Core Duo. Say for instance if you were to down grad a PC running Win 7 to Win XP the performance would appear much faster as the operating system is smaller and runs less software in the background. Often mistaken by Mac users compering there Mac to a PC.
If you can get back to me with more description on the build of your system I maybe of more use to you.
As for now my only tip I can offer is install TuneUp Utilities. TuneUp gives you the ability to close all unnecessary software running in the background. giving priority to the programs you are using.