You wonder if 256 +512 is better than 256+256?
Of course - provided you can use memory sticks of different size. This is not always (but mostly) the case
and provided the laptop supports more than 512 - there's quite a risk it does not
And I agree with Carlos - dual channel is good but...
And i'm not sure if there even is dual channel
Check the manual for the laptop
1.5 ghz is ok but not much more
I have removed the double post - that happens by accident occasionally and you can remove your own posts