How to identify my motherboard model number
its hard to find the ram 1066 MHz is there any other compatible ram?
For your asus notebook, you can find compatible memory here:
http://www.crucial.com/usa/en/compatible-upgrade-for/ASUS/k42ja RAM & SSD Upgrades | ASUS K42Ja | Crucial.com
The above link is provided for your convenience.
That's correct the ram compatible with your Laptop will be defined by your computer manufacturer.
The website Al Hill provided has the RAMs you need for your computer.