intel core 2 duo is best for hard core gaming. the AMD athlon one is average but still really good for a lot of gaming. Intel Pentium D is the average processor and for the things you said you needed it for, intel pentium d will be the most efficient and cheapest alternative.
Of the Intel Pentium D, Intel Core 2 Duo, and the AMD 64 X2 is better for just general use in a home computer used for music, internet, school work, powerpoint, and a little light gaming?
It seems that these are the most popular in the computers on the market today and the differences confuse me.